Add full traceback and SDK version logging for AssertionError debug

This will help identify where exactly the AssertionError is occurring
in the google-genai SDK and what version is installed on the server.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/services/llm_service.py

@@ -10,6 +10,7 @@ import json
 import asyncio
 import logging
 import base64
+import traceback
 from google import genai
 from google.genai import errors as genai_errors
 from openai import AsyncOpenAI
@@ -30,6 +31,10 @@ def get_gemini_client():
     when caching clients in ASGI environments where requests may come on different
     event loops. The overhead is minimal compared to the LLM API call.
     """
+    # Log SDK version on first call for debugging
+    import google.genai as genai_pkg
+    if hasattr(genai_pkg, '__version__'):
+        logger.info(f"google-genai SDK version: {genai_pkg.__version__}")
     return genai.Client(api_key=GEMINI_API_KEY)
 
 
@@ -307,8 +312,10 @@ class LLMService:
                 exc_repr = repr(e)
                 exc_args = getattr(e, 'args', ())
                 exc_dict = getattr(e, '__dict__', {})
+                exc_tb = traceback.format_exc()
 
                 logger.warning(f"LLM attempt {attempt_num}/{max_retries} failed - Type: {exc_module}.{exc_type}, str: '{exc_str}', repr: {exc_repr}, args: {exc_args}, dict: {exc_dict}")
+                logger.warning(f"Full traceback:\n{exc_tb}")
 
                 error_message = exc_str.lower() if exc_str else exc_repr.lower()