feat(v2): add PTY backend with portable-pty

- Implement PtyManager: spawn, write, resize, kill operations
- Wire Tauri commands: pty_spawn, pty_write, pty_resize, pty_kill
- Reader thread streams PTY output via Tauri events (pty-data-{id})
- Process exit detection emits pty-exit-{id} event
- Add portable-pty 0.8 and uuid 1.0 dependencies

v2/src-tauri/Cargo.toml

@@ -22,3 +22,5 @@ serde = { version = "1.0", features = ["derive"] }
 log = "0.4"
 tauri = { version = "2.10.3", features = [] }
 tauri-plugin-log = "2"
+portable-pty = "0.8"
+uuid = { version = "1", features = ["v4"] }