Migrate frontend to unified conversation API endpoints

## Overview

This issue tracks the frontend migration from the deprecated `/api/chat` endpoints to the unified `/api/conversations` API after the Phase 4 Router Unification (PR #589).

## Context

- **Related Issue**: #558 (Phase 4 Router Unification)
- **Blocker For**: Removing deprecated `chat_router.py`
- **Depends On**: PR #589 must be merged first
- **Related**: Issue #593 (API router tests)

## What Changed in Backend (PR #589)

The following endpoints were unified into `/api/conversations`:

### Chat Endpoints → Conversation Endpoints Mapping

| Old Endpoint (`/api/chat`) | New Endpoint (`/api/conversations`) | Notes |
|------------------------------|---------------------------------------|-------|
| `POST /chat/{session_id}/message` | `POST /conversations/{session_id}/messages` | Message creation |
| `GET /chat/{session_id}/messages` | `GET /conversations/{session_id}/messages` | Message retrieval |
| `GET /chat/{session_id}/suggestions` | `GET /conversations/{session_id}/suggestions` | Question suggestions |
| `POST /chat/{session_id}/conversation-suggestions` | `POST /conversations/{session_id}/conversation-suggestions` | Smart suggestions |

**Note**: All endpoints maintain the same request/response schemas for backward compatibility.

## Frontend Files to Update

### 1. API Client Configuration (`frontend/src/services/apiClient.ts`)

**Current state** (assumed based on typical React/TypeScript setup):
```typescript
// Example endpoints to migrate
const CHAT_BASE = '/api/chat';

export const chatApi = {
  sendMessage: (sessionId: string, message: string) => 
    axios.post(`${CHAT_BASE}/${sessionId}/message`, { message }),
  
  getMessages: (sessionId: string) => 
    axios.get(`${CHAT_BASE}/${sessionId}/messages`),
  
  getSuggestions: (sessionId: string, currentMessage: string) => 
    axios.get(`${CHAT_BASE}/${sessionId}/suggestions`, { params: { current_message: currentMessage } }),
};
```

**Required changes**:
```typescript
// Update base URL
const CONVERSATIONS_BASE = '/api/conversations';

export const conversationApi = {
  sendMessage: (sessionId: string, message: string) => 
    axios.post(`${CONVERSATIONS_BASE}/${sessionId}/messages`, { message }),
  
  getMessages: (sessionId: string) => 
    axios.get(`${CONVERSATIONS_BASE}/${sessionId}/messages`),
  
  getSuggestions: (sessionId: string, currentMessage: string) => 
    axios.get(`${CONVERSATIONS_BASE}/${sessionId}/suggestions`, { params: { current_message: currentMessage } }),
};
```

### 2. Component Updates

Search for all files importing/using chat API endpoints:

```bash
# Find all references to /api/chat in frontend
grep -r "/api/chat" frontend/src/

# Find all imports of chatApi or similar
grep -r "chatApi" frontend/src/
```

Common files that may need updates:
- `frontend/src/components/Chat/ChatInterface.tsx`
- `frontend/src/components/Chat/MessageList.tsx`
- `frontend/src/components/Chat/SuggestionPanel.tsx`
- `frontend/src/hooks/useChat.ts` (custom hook)
- `frontend/src/contexts/ChatContext.tsx` (context provider)

### 3. Type Definitions

Update any TypeScript interfaces referencing chat endpoints:

```typescript
// Before
interface ChatApiClient {
  sendMessage: (sessionId: string, message: string) => Promise<MessageResponse>;
  getMessages: (sessionId: string) => Promise<Message[]>;
}

// After
interface ConversationApiClient {
  sendMessage: (sessionId: string, message: string) => Promise<MessageResponse>;
  getMessages: (sessionId: string) => Promise<Message[]>;
}
```

## Implementation Plan

### Step 1: Create API Migration Layer (Recommended Approach)

Add a compatibility layer to support gradual migration:

```typescript
// frontend/src/services/conversationApi.ts (new file)
import axios from 'axios';

const BASE_URL = '/api/conversations';

export const conversationApi = {
  // Message operations
  sendMessage: async (sessionId: string, message: string) => {
    return axios.post(`${BASE_URL}/${sessionId}/messages`, { message });
  },

  getMessages: async (sessionId: string, limit?: number) => {
    return axios.get(`${BASE_URL}/${sessionId}/messages`, { params: { limit } });
  },

  // Suggestion operations
  getSuggestions: async (sessionId: string, currentMessage: string, maxSuggestions = 3) => {
    return axios.get(`${BASE_URL}/${sessionId}/suggestions`, {
      params: { current_message: currentMessage, max_suggestions: maxSuggestions }
    });
  },

  getConversationSuggestions: async (sessionId: string, suggestionInput: ConversationSuggestionInput) => {
    return axios.post(`${BASE_URL}/${sessionId}/conversation-suggestions`, suggestionInput);
  },
};
```

### Step 2: Update Component Imports

```typescript
// Before
import { chatApi } from '@/services/apiClient';

// After
import { conversationApi } from '@/services/conversationApi';
```

### Step 3: Update API Calls

```typescript
// Before
const messages = await chatApi.getMessages(sessionId);

// After
const messages = await conversationApi.getMessages(sessionId);
```

### Step 4: Testing Checklist

- [ ] **Message sending**: Verify messages are created and displayed correctly
- [ ] **Message retrieval**: Verify conversation history loads properly
- [ ] **Suggestions**: Verify question suggestions appear as expected
- [ ] **Smart suggestions**: Verify conversation-aware suggestions work
- [ ] **Error handling**: Verify 404/401/500 errors display user-friendly messages
- [ ] **Loading states**: Verify spinners/skeletons appear during API calls
- [ ] **Session management**: Verify session creation and switching works

### Step 5: Remove Old Chat API References

After verification, remove deprecated imports:

```bash
# Search for any remaining /api/chat references
grep -r "/api/chat" frontend/src/

# Remove old chatApi.ts if it exists
rm frontend/src/services/chatApi.ts
```

## Acceptance Criteria

- [ ] All frontend API calls updated to use `/api/conversations` endpoints
- [ ] No references to `/api/chat` remain in frontend code
- [ ] All chat features work correctly with new endpoints:
  - [ ] Message sending and receiving
  - [ ] Message history retrieval
  - [ ] Question suggestions
  - [ ] Smart conversation suggestions
- [ ] Error handling works correctly (404, 401, 500 responses)
- [ ] Loading states display properly during API calls
- [ ] No console errors or warnings in browser dev tools
- [ ] Frontend integration tests pass (if they exist)
- [ ] Manual testing completed across all chat features

## Estimated Effort

**2-3 hours** (depending on frontend codebase size)

- 30 min: Search and identify all `/api/chat` references
- 1 hour: Update API client and component imports
- 30 min: Update type definitions
- 1 hour: Manual testing and verification

## Testing Strategy

### Manual Testing

1. **Create new conversation session**
   - Verify session creation works
   - Verify session appears in session list

2. **Send messages**
   - Send user message
   - Verify assistant response appears
   - Verify message history updates

3. **Test suggestions**
   - Verify question suggestions load
   - Click suggestion and verify it populates input
   - Verify smart suggestions work with context

4. **Test error scenarios**
   - Invalid session ID → 404 error
   - Unauthenticated request → 401 error
   - Server error → 500 error with user-friendly message

### Automated Testing (if frontend tests exist)

```typescript
// Example test update
describe('ConversationApi', () => {
  it('should send message to correct endpoint', async () => {
    const sessionId = 'test-session-123';
    const message = 'Hello, world\!';
    
    await conversationApi.sendMessage(sessionId, message);
    
    expect(mockAxios.post).toHaveBeenCalledWith(
      '/api/conversations/test-session-123/messages',
      { message: 'Hello, world\!' }
    );
  });
});
```

## Migration Safety

**Backward Compatibility**: The backend maintains the same request/response schemas, so this is a **low-risk** migration. The only changes are:
- URL path (`/api/chat` → `/api/conversations`)
- Endpoint names (`/message` → `/messages`)

**Rollback Plan**: If issues arise, the deprecated `chat_router.py` remains functional until this migration is verified.

## Follow-up Tasks

After this migration is complete:
- [ ] Verify Issue #593 (API router tests) is complete
- [ ] Remove deprecated `backend/rag_solution/router/chat_router.py`
- [ ] Update API documentation to remove `/api/chat` references
- [ ] Close Issue #558 (Phase 4 Router Unification)

## Priority

**Medium-High** - Required to complete Phase 4 Router Unification, but not blocking current functionality (deprecated endpoints still work).

## Labels

- `frontend`
- `enhancement`
- `chat`

Old Endpoint (`/api/chat`)	New Endpoint (`/api/conversations`)	Notes
`POST /chat/{session_id}/message`	`POST /conversations/{session_id}/messages`	Message creation
`GET /chat/{session_id}/messages`	`GET /conversations/{session_id}/messages`	Message retrieval
`GET /chat/{session_id}/suggestions`	`GET /conversations/{session_id}/suggestions`	Question suggestions
`POST /chat/{session_id}/conversation-suggestions`	`POST /conversations/{session_id}/conversation-suggestions`	Smart suggestions

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Migrate frontend to unified conversation API endpoints #594

Overview

Context

What Changed in Backend (PR #589)

Chat Endpoints → Conversation Endpoints Mapping

Frontend Files to Update

1. API Client Configuration (`frontend/src/services/apiClient.ts`)

2. Component Updates

3. Type Definitions

Implementation Plan

Step 1: Create API Migration Layer (Recommended Approach)

Step 2: Update Component Imports

Step 3: Update API Calls

Step 4: Testing Checklist

Step 5: Remove Old Chat API References

Acceptance Criteria

Estimated Effort

Testing Strategy

Manual Testing

Automated Testing (if frontend tests exist)

Migration Safety

Follow-up Tasks

Priority

Labels

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Migrate frontend to unified conversation API endpoints #594

Description

Overview

Context

What Changed in Backend (PR #589)

Chat Endpoints → Conversation Endpoints Mapping

Frontend Files to Update

1. API Client Configuration (frontend/src/services/apiClient.ts)

2. Component Updates

3. Type Definitions

Implementation Plan

Step 1: Create API Migration Layer (Recommended Approach)

Step 2: Update Component Imports

Step 3: Update API Calls

Step 4: Testing Checklist

Step 5: Remove Old Chat API References

Acceptance Criteria

Estimated Effort

Testing Strategy

Manual Testing

Automated Testing (if frontend tests exist)

Migration Safety

Follow-up Tasks

Priority

Labels

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions

1. API Client Configuration (`frontend/src/services/apiClient.ts`)