fix: Use invoke() instead of deprecated get_relevant_documents()

- Fixed AttributeError: 'RerankingRetriever' object has no attribute 'get_relevant_documents'
- Replaced deprecated LangChain method calls with .invoke()
- Kept context enhancements (top-30 files, file tree, full content)

code_chatbot/rag.py

@@ -414,7 +414,8 @@ class ChatEngine:
             query_for_retrieval = f"{self.chat_history[-1].content} {question}"
             
         # Increase retrieval limit to 30 docs since Gemini has large context
-        docs = self.retriever.get_relevant_documents(query_for_retrieval)
+        # FIXED: Use .invoke() instead of .get_relevant_documents() (deprecated/removed in LC 0.1)
+        docs = self.retriever.invoke(query_for_retrieval)
         
         if not docs:
             # Return empty context if no docs found