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/__tests__/createGatewayEventHandler.test.ts

@@ -15,7 +15,8 @@ const buildCtx = (appended: Msg[]) =>
     composer: {
       dequeue: () => undefined,
       queueEditRef: ref<null | number>(null),
-      sendQueued: vi.fn()
+      sendQueued: vi.fn(),
+      setInput: vi.fn()
     },
     gateway: {
       gw: { request: vi.fn() },
@@ -29,6 +30,9 @@ const buildCtx = (appended: Msg[]) =>
       resumeById: vi.fn(),
       setCatalog: vi.fn()
     },
+    submission: {
+      submitRef: { current: vi.fn() }
+    },
     system: {
       bellOnComplete: false,
       sys: vi.fn()
@@ -38,6 +42,11 @@ const buildCtx = (appended: Msg[]) =>
       panel: (title: string, sections: any[]) =>
         appended.push({ kind: 'panel', panelData: { sections, title }, role: 'system', text: '' }),
       setHistoryItems: vi.fn()
+    },
+    voice: {
+      setProcessing: vi.fn(),
+      setRecording: vi.fn(),
+      setVoiceEnabled: vi.fn()
     }
   }) as any