feat: add enable_web_search config to disable web search (#681) (#760)

* feat: add enable_web_search config to disable web search (#681)

* fix: skip enforce_researcher_search validation when web search is disabled

- Return json.dumps([]) instead of empty string for consistency in background_investigation_node

- Add enable_web_search check to skip validation warning when user intentionally disabled web search

- Add warning log when researcher has no tools available

- Update tests to include new enable_web_search parameter

* fix: address Copilot review feedback

- Coordinate enforce_web_search with enable_web_search in validate_and_fix_plan

- Fix misleading comment in background_investigation_node

* docs: add warning about local RAG setup when disabling web search

* docs: add web search toggle section to configuration guide

src/server/chat_request.py

@@ -62,6 +62,9 @@ class ChatRequest(BaseModel):
     enable_background_investigation: Optional[bool] = Field(
         True, description="Whether to get background investigation before plan"
     )
+    enable_web_search: Optional[bool] = Field(
+        True, description="Whether to enable web search, set to False to use only local RAG"
+    )
     report_style: Optional[ReportStyle] = Field(
         ReportStyle.ACADEMIC, description="The style of the report"
     )