refactor(aisidebar): restructure project and implement reasoning mode toggle

- Reorganize project structure and file locations
- Add ReasoningController to manage model selection and reasoning mode
- Update design and requirements for reasoning mode toggle
- Implement model switching between Qwen3-4B-Instruct and Qwen3-4B-Thinking models
- Remove deprecated files and consolidate project layout
- Add new steering and specification documentation
- Clean up and remove unnecessary files and directories
- Prepare for enhanced AI sidebar functionality with more flexible model handling

conversation_manager.py

@@ -102,6 +102,39 @@ class ConversationManager:
         self._state.updated_at = now
         self._write_state()
 
+    def clear_messages(self) -> None:
+        """Clear all messages and reset the conversation state."""
+        timestamp = datetime.now(timezone.utc).isoformat()
+        self._state = ConversationState(
+            conversation_id=self._conversation_id,
+            created_at=timestamp,
+            updated_at=timestamp,
+            messages=[],
+        )
+        self._write_state()
+    
+    def trim_to_recent(self, keep_count: int = 20) -> List[Dict[str, str]]:
+        """Trim conversation to keep only recent messages, return removed messages.
+        
+        Args:
+            keep_count: Number of recent messages to keep
+            
+        Returns:
+            List of messages that were removed (older messages)
+        """
+        if len(self._state.messages) <= keep_count:
+            return []
+        
+        # Split messages into old and recent
+        removed_messages = self._state.messages[:-keep_count]
+        self._state.messages = self._state.messages[-keep_count:]
+        
+        # Update state and persist
+        self._state.updated_at = datetime.now(timezone.utc).isoformat()
+        self._write_state()
+        
+        return removed_messages
+
     # ------------------------------------------------------------------ persistence
     def _load_state(self) -> ConversationState:
         """Load the transcript from disk or create a fresh default."""