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/app/useMainApp.ts

@@ -454,13 +454,20 @@ export function useMainApp(gw: GatewayClient) {
     composer: { actions: composerActions, refs: composerRefs, state: composerState },
     gateway,
     terminal: { hasSelection, scrollRef, scrollWithSelection, selection, stdout },
-    voice: { recording: voiceRecording, setProcessing: setVoiceProcessing, setRecording: setVoiceRecording },
+    voice: {
+      enabled: voiceEnabled,
+      recording: voiceRecording,
+      setProcessing: setVoiceProcessing,
+      setRecording: setVoiceRecording,
+      setVoiceEnabled
+    },
     wheelStep: WHEEL_SCROLL_STEP
   })
 
   const onEvent = useMemo(
     () =>
       createGatewayEventHandler({
+        composer: { setInput: composerActions.setInput },
         gateway,
         session: {
           STARTUP_RESUME_ID,
@@ -470,18 +477,29 @@ export function useMainApp(gw: GatewayClient) {
           resumeById: session.resumeById,
           setCatalog
         },
+        submission: { submitRef },
         system: { bellOnComplete, stdout, sys },
-        transcript: { appendMessage, panel, setHistoryItems }
+        transcript: { appendMessage, panel, setHistoryItems },
+        voice: {
+          setProcessing: setVoiceProcessing,
+          setRecording: setVoiceRecording,
+          setVoiceEnabled
+        }
       }),
     [
       appendMessage,
       bellOnComplete,
+      composerActions.setInput,
       gateway,
       panel,
       session.newSession,
       session.resetSession,
       session.resumeById,
+      setVoiceEnabled,
+      setVoiceProcessing,
+      setVoiceRecording,
       stdout,
+      submitRef,
       sys
     ]
   )