feat: replace Agent mode with independent Tools toggle

- Remove 'agent' from mode dropdown; Chat/Note/OTR remain
- Add ⚡ tools toggle button in input bar (persisted in localStorage)
  When on: routes to POST /orchestrate (Gemini tool loop); send btn → "Run"
  When off: routes to POST /chat (direct to active role); no change
- Role selector and tools toggle are now fully independent:
  active chat_role sent in orchestrate payload → used for final response
- orchestrator_engine.run() accepts response_role param; passes it to
  complete(role=...) instead of hardcoded model="claude"
- OrchestrateRequest gains chat_role field (default "chat")
- Migrate stored 'agent' mode/MRU entries to 'chat' on load

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/routers/orchestrator.py

@@ -52,6 +52,7 @@ class OrchestrateRequest(BaseModel):
     include_short: bool = True
     user: str = "scott"
     persona: str = "inara"
+    chat_role: str = "chat"             # role used for the final response (decoupled from tool-loop model)
 
 
 class OrchestrateResponse(BaseModel):
@@ -184,6 +185,7 @@ async def _run_job(job_id: str, req: OrchestrateRequest, user: str) -> None:
                 respond_with_claude=req.respond_with_claude,
                 gemini_api_key=gemini_key,
                 model_name=orch_model.get("model_name") if orch_model else None,
+                response_role=req.chat_role,
             )
 
         # Save the turn to the session store so it survives a page refresh