Fix: Reranker fails with missing template - needs fallback or template seeding

[manavgup]

Problem

When reranking is enabled (ENABLE_RERANKING=True, which is the default), the system fails with:

ValueError: Template is required for batch generation
  File: rag_solution/generation/providers/watsonx.py:218

Root Cause

1. Reranking is enabled by default in core/config.py:143
2. LLMReranker requires a PromptTemplateType.RERANKING template from database
3. No reranking template exists in database for users (not seeded during initialization)
4. Fallback to SimpleReranker exists in code but fails before it can trigger

Impact

• Severity: HIGH - Blocks all search operations when reranking enabled
• Workaround: Disable reranking (ENABLE_RERANKING=False)

Proposed Solutions

Option 1: Seed Default Reranking Template (Recommended)

Add reranking template to database initialization

Option 2: Hardcode Fallback Template

Add default template in LLMReranker.__init__()

Option 3: Better Fallback Logic

Fix SearchService.get_reranker() to catch template errors earlier

Files Involved

• backend/rag_solution/services/search_service.py:172-237
• backend/rag_solution/retrieval/reranker.py:60-84
• backend/rag_solution/generation/providers/watsonx.py:194-227
• backend/core/config.py:143

Temporary Fix Applied

Changed default to ENABLE_RERANKING=False in core/config.py:143