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

command_processor.py

@@ -0,0 +1,87 @@
+"""Command processing system for AI Sidebar slash commands."""
+
+from dataclasses import dataclass
+from typing import Callable, Optional
+
+
+@dataclass
+class CommandResult:
+    """Result of command execution."""
+    success: bool
+    message: str
+    data: dict | None = None
+
+
+class CommandProcessor:
+    """Parses and executes slash commands."""
+    
+    def __init__(self):
+        """Initialize command processor with command registry."""
+        self._handlers: dict[str, Callable] = {}
+        
+    def register_command(self, command: str, handler: Callable) -> None:
+        """
+        Register a command handler.
+        
+        Args:
+            command: Command string (e.g., "/new", "/model")
+            handler: Callable that takes command arguments and returns CommandResult
+        """
+        self._handlers[command.lower()] = handler
+    
+    def is_command(self, text: str) -> bool:
+        """
+        Check if text starts with a command.
+        
+        Args:
+            text: User input text
+            
+        Returns:
+            True if text starts with a registered command
+        """
+        if not text or not text.startswith("/"):
+            return False
+        
+        # Extract command (first word)
+        parts = text.strip().split(maxsplit=1)
+        command = parts[0].lower()
+        
+        return command in self._handlers
+    
+    def execute(self, text: str) -> CommandResult:
+        """
+        Parse and execute command.
+        
+        Args:
+            text: User input text starting with command
+            
+        Returns:
+            CommandResult with execution status and message
+        """
+        if not text or not text.startswith("/"):
+            return CommandResult(
+                success=False,
+                message="Invalid command format. Commands must start with '/'."
+            )
+        
+        # Parse command and arguments
+        parts = text.strip().split(maxsplit=1)
+        command = parts[0].lower()
+        args = parts[1] if len(parts) > 1 else ""
+        
+        # Check if command is registered
+        if command not in self._handlers:
+            return CommandResult(
+                success=False,
+                message=f"Unknown command: {command}. Type /help for available commands."
+            )
+        
+        # Execute command handler
+        try:
+            handler = self._handlers[command]
+            return handler(args)
+        except Exception as e:
+            return CommandResult(
+                success=False,
+                message=f"Error executing command: {str(e)}"
+            )