feat(capture): swap the rdev fork for keytap 0.2, delete local chord state machine

Dep swap:
- Drop the git-pinned jamiepine/rdev fork we were carrying since the
  upstream crate is abandoned.
- Depend on keytap 0.2 from crates.io — our own cross-platform global
  keyboard tap crate. Clean shutdown via Drop, Sonoma-safe by design
  (no TSMGetInputSourceProperty calls off the main thread, so
  `set_is_main_thread(false)` is gone), and properly versioned.

Chord engine rewrite:
- Delete hotkey_monitor.rs's internal Chord state machine (Match enum,
  KeyEvent enum, step()/classify() methods, associated unit tests).
  keytap's ChordMatcher subsumes it: Momentary chord for PTT,
  add_toggle() for Toggle-to-talk, longest-match resolution, sticky-end
  for Toggle. Net: -80 LOC in hotkey_monitor.rs; the remaining module
  is the dispatcher loop + Effect→Tauri translation.
- Preserve the PTT→Toggle "RestartRecording" upgrade signal. keytap
  emits End(PTT)+Start(Toggle) atomically (same Instant) when the held
  set upgrades from a shorter chord to a longer superset. The
  dispatcher peeks at the matcher with a 5 ms recv_timeout after any
  End and coalesces the pair into Effect::RestartRecording so the
  frontend still gets the "discard the transition-moment audio" signal
  instead of an unrelated Stop+Start pair.
- HotkeyMonitor::update_bindings now actually tears down the tap on
  empty bindings instead of leaving an idle CGEventTap around. New
  bindings rebuild the matcher and the dispatcher thread from scratch.

key_codes.rs:
- Rewrite the browser-code → Key table against keytap's cleaner Key
  variant names (`A`..`Z` not `KeyA`..`KeyZ`, `Digit0`..`Digit9` not
  `Num0`..`Num9`, `ArrowUp` not `UpArrow`, `AltLeft`/`AltRight` instead
  of `Alt`/`AltGr`, `Period` not `Dot`, …). On-disk chord string
  format (W3C `KeyboardEvent.code` identifiers) is unchanged, so
  capture_settings rows written before the swap round-trip identically.
  Legacy aliases (`Alt`, `AltGr`, `Num0`, `UpArrow`, `Dot`, …) kept for
  forward-compat on old rows.

main.rs / input_monitoring.rs:
- Update the few doc comments that referenced `rdev::listen` to
  describe keytap's Tap; no behavioural change.
- build_chord_bindings now imports from keytap::Key.
- enable_hotkey / disable_hotkey / update_chord_bindings reach into
  HotkeyMonitor via &mut since apply()/update_bindings() now mutate.

Tests live in keytap now (22 chord-related tests in keytap 0.2,
including the PTT→Toggle upgrade scenario that used to be tested in
hotkey_monitor.rs). Voicebox's hotkey_monitor.rs is thin enough that
local testing would be trivia.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

tauri/src-tauri/src/input_monitoring.rs

@@ -2,8 +2,8 @@
 //!
 //! On macOS 10.15+, creating a CGEventTap that observes keyboard events
 //! requires the host process to be listed under System Settings → Privacy &
-//! Security → Input Monitoring. Without that trust, `rdev::listen` returns
-//! immediately and no key events ever flow through the chord engine.
+//! Security → Input Monitoring. Without that trust, keytap's `Tap` returns
+//! a permission error and no key events ever flow through the chord engine.
 //!
 //! The relevant TCC pair lives in IOKit, mirroring `AXIsProcessTrusted` /
 //! `AXIsProcessTrustedWithOptions` on the Accessibility side:
@@ -20,7 +20,7 @@
 //!
 //! `enable_hotkey` calls `request` on first invocation so the prompt fires
 //! from a deterministic, user-initiated point (the Captures toggle) instead
-//! of as a side-effect of `rdev::listen` creating its CGEventTap.
+//! of as a side-effect of keytap's `Tap` creating its CGEventTap.
 //!
 //! Windows / Linux don't gate keyboard taps behind a TCC-style permission,
 //! so those branches return `true`.