feat(Track): Add central command dispatcher for frontend and sidecar requests

- Implements core routing hub for Mountain component handling commands from Sky (Tauri invoke) and Cocoon (Vine IPC)
- Provides dispatch_command Tauri function for frontend interactions and dispatch_sidecar_request for extension host communications
- Maps commands to ActionEffects using Land_Common effect constructors or routes to direct handler/RPC methods
- Integrates with AppRuntime for effect execution and AppState for context
- Implements error handling and logging for both frontend and sidecar request paths
- Supports terminal environment operations, extension lifecycle events, and VS Code-compatible RPC methods
- Enables critical path for extension-host communication while maintaining performance through Rust-native routing
- Provides foundation for effect-based architecture that will scale with additional extension capabilities

Author: NikolaRHristov