Fix: Include inputSchema in tools/list responses to prevent client parameter wrapping

[Copilot]

Clients were wrapping tool parameters in a "data" field (e.g., {"arguments":{"data":{"body":"...)) because the gateway was omitting inputSchema` from tools/list responses. Without schema information, clients couldn't understand parameter structure.

Root Cause

The gateway intentionally omitted inputSchema when registering tools to avoid JSON Schema version conflicts (draft-07 from backends vs draft-2020-12 required by SDK validation). This left clients unable to parse tool parameter requirements.

Changes

Switch to non-validating tool registration:

• Use server.AddTool (method, no validation) instead of sdk.AddTool (function, validates)
• Include inputSchema from backends regardless of JSON Schema version
• Apply consistently across unified and routed modes

Handle missing schemas:

• NormalizeInputSchema now provides default empty object schema when backend returns nil
• Satisfies SDK requirement that inputSchema must exist with type "object"

Example

Before (tools/list response):

{
  "tools": [{
    "name": "create_output",
    "description": "Create an output"
    // inputSchema missing - client guesses wrong
  }]
}

After:

{
  "tools": [{
    "name": "create_output",
    "description": "Create an output",
    "inputSchema": {
      "type": "object",
      "properties": {
        "body": {"type": "string"}
      }
    }
  }]
}

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