Fix remaining f-string syntax errors

- Fix 'end' and 'error' data serialization
- Extract all dict literals outside f-strings

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

main.py

@@ -450,10 +450,12 @@ async def chat_stream(request: ChatRequest):
             # Log interaction
             log_interaction(session_id, request.message, len(full_response))
 
-            yield f"data: {json.dumps({'type': 'end'})}\n\n"
+            end_data = {'type': 'end'}
+            yield f"data: {json.dumps(end_data)}\n\n"
 
         except Exception as e:
-            yield f"data: {json.dumps({'type': 'error', 'message': str(e)})}\n\n"
+            error_data = {'type': 'error', 'message': str(e)}
+            yield f"data: {json.dumps(error_data)}\n\n"
         finally:
             # Always return the model to the pool
             if model is not None: