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/interfaces.ts

@@ -189,9 +189,11 @@ export interface InputHandlerContext {
     stdout?: NodeJS.WriteStream
   }
   voice: {
+    enabled: boolean
     recording: boolean
     setProcessing: StateSetter<boolean>
     setRecording: StateSetter<boolean>
+    setVoiceEnabled: StateSetter<boolean>
   }
   wheelStep: number
 }
@@ -201,6 +203,9 @@ export interface InputHandlerResult {
 }
 
 export interface GatewayEventHandlerContext {
+  composer: {
+    setInput: StateSetter<string>
+  }
   gateway: GatewayServices
   session: {
     STARTUP_RESUME_ID: string
@@ -210,6 +215,9 @@ export interface GatewayEventHandlerContext {
     resumeById: (id: string) => void
     setCatalog: StateSetter<null | SlashCatalog>
   }
+  submission: {
+    submitRef: MutableRefObject<(value: string) => void>
+  }
   system: {
     bellOnComplete: boolean
     stdout?: NodeJS.WriteStream
@@ -220,6 +228,11 @@ export interface GatewayEventHandlerContext {
     panel: (title: string, sections: PanelSection[]) => void
     setHistoryItems: StateSetter<Msg[]>
   }
+  voice: {
+    setProcessing: StateSetter<boolean>
+    setRecording: StateSetter<boolean>
+    setVoiceEnabled: StateSetter<boolean>
+  }
 }
 
 export interface SlashHandlerContext {