feat(voice): first-class voice input and local TTS across web, desktop, and mobile (#2018)

Complete rebuild of voice input on a server-authoritative streaming
architecture, replacing the legacy Web Speech / whole-blob / WASM engines
and the dead voice-agent layer (~4k lines removed).

Speech-to-text (dictation):
- Client streams 16 kHz mono PCM16 chunks over /api/dictation/ws with
  seq/ack ordering; buffered audio is retained and replayed on reconnect
- Server transcribes and streams live partial transcripts back;
  segments auto-commit every ~15s with silence suppression and adaptive
  finalization timeouts
- Local provider (default, zero config): sherpa-onnx models in a forked
  worker process — auto-download with progress, staged extraction with
  verification, corrupt-model auto-recovery, idle shutdown after 5 min
- Model catalog with settings picker (accuracy/speed ratings, sizes,
  download/delete): Parakeet TDT v2 (English) and v3 (25 European
  languages, auto-detected), Whisper base and tiny (multilingual, light)
- OpenAI-compatible provider for any Whisper endpoint
- Composer overlay with live transcript, volume meter, timer, and
  cancel / insert / insert-and-send actions; failed transcriptions keep
  their audio for retry or accepting the partial text as-is
- Configurable keyboard shortcut (default mod+alt+v) toggles dictation;
  Enter confirms and Escape cancels while recording
- Overlay is pixel-aligned with the composer (measured footer height,
  matching paddings/typography/gaps) — no layout shift when toggling

Text-to-speech:
- Local Kokoro provider (English, 11 voices) synthesized in the same
  worker via /api/dictation/tts/speak, managed by the shared model
  pipeline; sentence-pipelined playback keeps time-to-first-audio at
  ~1 sentence regardless of message length, and stop cancels in-flight
  synthesis
- Sanitizer keeps inline-code content (strips backticks only), reads
  interword slashes aloud, and removes only absolute file paths

Settings:
- Voice page unified: a single read-aloud toggle owns all playback
  options (the confusing "Enable Voice Mode" is gone); a new "Enable
  voice input" toggle (default on, persisted to settings.json) hides
  the composer mic entirely when disabled

Mobile and transport:
- iOS/Android microphone permissions added (dictation was previously
  impossible on mobile)
- Fixed Android WebSocket upgrades: the Capacitor WebView origin
  (https://localhost) was missing from the packaged-client allowlist,
  403-ing every WS connection — root cause of the old mobile SSE lock,
  which is now removed for all transports

Security and conventions:
- All HTTP routes sit behind the global /api auth gate; the WS upgrade
  explicitly validates the UI session and origin, with oc_url_token
  narrowly allowlisted and covered by tests; the dictation socket mints
  a fresh URL token before connecting
- Routes register before the generic OpenCode proxy; the client goes
  through runtimeFetch/getRuntimeUrlResolver, and runtime switches
  reset the dictation socket
- VS Code deliberately reports dictation as unavailable (no server
  process in that runtime)

CI: workflow Node bumped 20 -> 22 to match the repo engines and fix
better-sqlite3 installs broken by node-gyp@latest on Node 20.

New dependency: sherpa-onnx-node (prebuilt N-API; macOS/Linux x64+arm64,
Windows x64 — Windows-on-ARM falls back to the OpenAI-compatible provider)

packages/web/server/index.js

@@ -38,6 +38,7 @@ import { prepareNotificationLastMessage } from './lib/notifications/index.js';
 import { registerTtsRoutes } from './lib/tts/routes.js';
 import { detectSayTtsCapability } from './lib/tts/capability-runtime.js';
 import { createTerminalRuntime } from './lib/terminal/runtime.js';
+import { createDictationRuntime } from './lib/dictation/runtime.js';
 import {
   createGlobalUiEventBroadcaster,
   createGlobalMessageStreamHub,
@@ -495,6 +496,7 @@ const tunnelAuthController = createTunnelAuth();
 let runtimeManagedRemoteTunnelToken = '';
 let runtimeManagedRemoteTunnelHostname = '';
 let terminalRuntime = null;
+let dictationRuntime = null;
 let messageStreamRuntime = null;
 const userProvidedOpenCodePassword = hmrStateRuntime.getUserProvidedOpenCodePassword(hmrState);
 const initialOpenCodeAuthState = hmrStateRuntime.resolveOpenCodeAuthFromState({
@@ -898,6 +900,7 @@ const tunnelWiringRuntime = createTunnelWiringRuntime({
 });
 const startupPipelineRuntime = createStartupPipelineRuntime({
   createTerminalRuntime,
+  createDictationRuntime,
   createMessageStreamWsRuntime,
   createServerStartupRuntime,
 });
@@ -1357,8 +1360,10 @@ async function main(options = {}) {
     tunnelRuntimeContext,
     attachSignals,
     apiOnly,
+    dictationModelsDir: path.join(OPENCHAMBER_USER_CONFIG_ROOT, 'speech-models'),
   });
   terminalRuntime = startupPipelineResult.terminalRuntime;
+  dictationRuntime = startupPipelineResult.dictationRuntime;
   messageStreamRuntime = startupPipelineResult.messageStreamRuntime;
 
   try {
@@ -1397,6 +1402,11 @@ async function main(options = {}) {
     },
     stop: (shutdownOptions = {}) => {
       realtimeProxyRuntime.stop();
+      try {
+        dictationRuntime?.stop?.();
+      } catch {
+        // best-effort shutdown of the dictation worker
+      }
       return gracefulShutdown({ exitProcess: shutdownOptions.exitProcess ?? false });
     }
   };