Fix f-string syntax error in streaming endpoint

- Extract dict construction outside f-string
- Fixes SyntaxError with nested braces in json.dumps

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

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

main.py

@@ -428,7 +428,14 @@ async def chat_stream(request: ChatRequest):
 
             # Send initial metadata with pool stats
             pool_stats = model_pool.get_stats()
-            yield f"data: {json.dumps({{'type': 'start', 'session_id': session_id, 'model': MODEL_REPO, 'interaction_count': count, 'pool_available': pool_stats['available']})}\n\n"
+            start_data = {
+                'type': 'start',
+                'session_id': session_id,
+                'model': MODEL_REPO,
+                'interaction_count': count,
+                'pool_available': pool_stats['available']
+            }
+            yield f"data: {json.dumps(start_data)}\n\n"
 
             # Stream tokens
             for token in model.generate_stream(
@@ -436,7 +443,8 @@ async def chat_stream(request: ChatRequest):
                     max_tokens=request.max_tokens
             ):
                 full_response += token
-                yield f"data: {json.dumps({'type': 'token', 'content': token})}\n\n"
+                token_data = {'type': 'token', 'content': token}
+                yield f"data: {json.dumps(token_data)}\n\n"
                 await asyncio.sleep(0)
 
             # Log interaction