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/Cargo.toml

@@ -31,6 +31,11 @@ tar = "0.4"
 reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"] }
 iana-time-zone = "0.1"
 sha2 = "0.10"
+axum = { version = "0.8", features = ["ws"] }
+tower-http = { version = "0.6", features = ["cors"] }
+base64 = "0.22"
+rand = "0.9"
+local-ip-address = "0.6"
 
 [build-dependencies]
 tauri-build = { version = "2", features = [] }