Add MCP server for council integration

- Add mcp_server package with 7 tools proxying to FastAPI:
  - council_query (full 3-stage process)
  - council_stage1_collect, stage2_rank, stage3_synthesize
  - council_conversation_create, list, get
- Add individual stage endpoints to FastAPI (/api/council/stage1, stage2, stage3)
- Update council models to use valid OpenRouter identifiers
- Add mcp>=1.0.0 dependency

backend/config.py

@@ -10,10 +10,10 @@ OPENROUTER_API_KEY = os.getenv("OPENROUTER_API_KEY")
 
 # Council members - list of OpenRouter model identifiers
 COUNCIL_MODELS = [
-    "openai/gpt-5.1",
+    "openai/gpt-4o",
     "google/gemini-3-pro-preview",
     "anthropic/claude-sonnet-4.5",
-    "x-ai/grok-4",
+    "x-ai/grok-4.1-fast",
 ]
 
 # Chairman model - synthesizes final response