Add web terminal for remote tablet/phone access to project terminals

Adds an axum HTTP+WebSocket server that runs alongside the Tauri app,
serving a standalone xterm.js-based terminal UI accessible from any
browser on the local network. Shares the existing ExecSessionManager
via Arc-wrapped stores, with token-based authentication and automatic
session cleanup on disconnect.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src-tauri/src/web_terminal/mod.rs

@@ -0,0 +1,4 @@
+pub mod server;
+mod ws_handler;
+
+pub use server::WebTerminalServer;