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.lock

@@ -91,6 +91,9 @@ name = "bitflags"
 version = "2.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4388bee8683e3d04af747c73422af53102d2bd24d9eadb6cbc100baef4b43f8"
+dependencies = [
+ "serde_core",
+]
 
 [[package]]
 name = "block-buffer"
@@ -219,6 +222,7 @@ dependencies = [
  "mio",
  "parking_lot",
  "rustix",
+ "serde",
  "signal-hook",
  "signal-hook-mio",
  "winapi",