Full remote input parity: forward mouse and structured key events over IPC

- New key_event/mouse_event client messages (crossterm serde) that run
  through the complete WM event handling on the server — remote clients
  get window focus, drag/resize and mouse forwarding into virtual
  terminals (SGR/UTF-8/X10) identical to standalone mode
- tui-wm -c now forwards mouse events; previously only keyboard worked
  remotely
- IPC unit tests + end-to-end integration test (tests/integration.py):
  daemon, frames, click/scroll SGR forwarding, popups, TUI-FM in a
  window — 12/12 passing
- Document the new messages in SOCKET_API.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Cargo.toml

@@ -8,7 +8,7 @@ name = "tui-wm"
 path = "src/main.rs"
 
 [dependencies]
-crossterm = { version = "0.29", features = ["event-stream"] }
+crossterm = { version = "0.29", features = ["event-stream", "serde"] }
 ratatui = "0.30"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"