feat(tui): match CLI's voice slash + VAD-continuous recording model

The TUI had drifted from the CLI's voice model in two ways:

- /voice on was lighting up the microphone immediately and Ctrl+B was
  interpreted as a mode toggle.  The CLI separates the two: /voice on
  just flips the umbrella bit, recording only starts once the user
  presses Ctrl+B, which also sets _voice_continuous so the VAD loop
  auto-restarts until the user presses Ctrl+B again or three silent
  cycles pass.
- /voice tts was missing entirely, so users couldn't turn agent reply
  speech on/off from inside the TUI.

This commit brings the TUI to parity.

Python

- hermes_cli/voice.py: continuous-mode API (start_continuous,
  stop_continuous, is_continuous_active) layered on the existing PTT
  wrappers. The silence callback transcribes, fires on_transcript,
  tracks consecutive no-speech cycles, and auto-restarts — mirroring
  cli.py:_voice_stop_and_transcribe + _restart_recording.
- tui_gateway/server.py:
  - voice.toggle now supports on / off / tts / status.  The umbrella
    bit lives in HERMES_VOICE + display.voice_enabled; tts lives in
    HERMES_VOICE_TTS + display.voice_tts.  /voice off also tears down
    any active continuous loop so a toggle-off really releases the
    microphone.
  - voice.record start/stop now drives start_continuous/stop_continuous.
    start is refused with a clear error when the mode is off, matching
    cli.py:handle_voice_record's early return on `not _voice_mode`.
  - New voice.transcript / voice.status events emit through
    _voice_emit (remembers the sid that last enabled the mode so
    events land in the right session).

TypeScript

- gatewayTypes.ts: voice.status + voice.transcript event
  discriminants; VoiceToggleResponse gains tts; VoiceRecordResponse
  gains status for the new "started/stopped" responses.
- interfaces.ts: GatewayEventHandlerContext gains composer.setInput +
  submission.submitRef + voice.{setRecording, setProcessing,
  setVoiceEnabled}; InputHandlerContext.voice gains enabled +
  setVoiceEnabled for the mode-aware Ctrl+B handler.
- createGatewayEventHandler.ts: voice.status drives REC/STT badges;
  voice.transcript auto-submits when the composer is empty (CLI
  _pending_input.put parity) and appends when a draft is in flight.
  no_speech_limit flips voice off + sys line.
- useInputHandlers.ts: Ctrl+B now calls voice.record (start/stop),
  not voice.toggle, and nudges the user with a sys line when the
  mode is off instead of silently flipping it on.
- useMainApp.ts: wires the new event-handler context fields.
- slash/commands/session.ts: /voice handles on / off / tts / status
  with CLI-matching output ("voice: mode on · tts off").

Backward compat preserved for voice.record (was always PTT shape;
gateway still honours start/stop with mode-gating added).

ui-tui/src/gatewayTypes.ts

@@ -236,10 +236,16 @@ export interface ImageAttachResponse {
 // ── Voice ────────────────────────────────────────────────────────────
 
 export interface VoiceToggleResponse {
+  audio_available?: boolean
+  available?: boolean
+  details?: string
   enabled?: boolean
+  stt_available?: boolean
+  tts?: boolean
 }
 
 export interface VoiceRecordResponse {
+  status?: string
   text?: string
 }
 
@@ -368,6 +374,8 @@ export type GatewayEvent =
   | { payload?: { text?: string }; session_id?: string; type: 'thinking.delta' }
   | { payload?: undefined; session_id?: string; type: 'message.start' }
   | { payload?: { kind?: string; text?: string }; session_id?: string; type: 'status.update' }
+  | { payload?: { state?: 'idle' | 'listening' | 'transcribing' }; session_id?: string; type: 'voice.status' }
+  | { payload?: { no_speech_limit?: boolean; text?: string }; session_id?: string; type: 'voice.transcript' }
   | { payload: { line: string }; session_id?: string; type: 'gateway.stderr' }
   | { payload?: { cwd?: string; python?: string }; session_id?: string; type: 'gateway.start_timeout' }
   | { payload?: { preview?: string }; session_id?: string; type: 'gateway.protocol_error' }