Implement graceful shutdown for the server and enhance process management on Windows

- Added a new `/shutdown` endpoint to allow graceful server shutdown via HTTP.
- Implemented process tree management functions to handle child processes during shutdown on Windows.
- Updated the `stop_server` function to attempt graceful shutdown before forcefully terminating processes.
- Enhanced error handling and logging for shutdown operations.

tauri/src-tauri/Cargo.toml

@@ -20,6 +20,7 @@ tauri-plugin-shell = "2.0"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 tokio = { version = "1", features = ["full"] }
+reqwest = { version = "0.12", features = ["blocking", "json"] }
 hound = "3.5"
 base64 = "0.22"
 cpal = "0.15"