feat(errors): add Sentry observability behind a sinks facade

logError / reportError now route through a pair of sinks installed at
bootstrap by each process (main + every renderer entry). No call site
knows about Sentry — if sentryDsn is empty, the sinks simply aren't
installed and logError/reportError stay console-only.

- appConfig.sentryDsn: per-env string (empty for now — populate when
  ops creates the DSNs). Empty is the no-op mode for dev.
- lib/errors.ts: installErrorSinks({ capture, breadcrumb }) gates
  Sentry.captureException / Sentry.addBreadcrumb. Everything flows
  through toUserMessage and the two existing call types.
- lib/sentry.ts: initSentryRenderer() for the main window + autoplay,
  huddle, and screen-record renderers.
- main/sentry.ts: initSentryMain() runs before anything else in
  main.ts to catch bootstrap failures. Captures uncaught exceptions
  and the crash reporter automatically.
- main/ipc-utils.ts::safeHandle now routes through reportError.
- main.ts::fetchLinkMetadata logs via logError.

js/package.json

@@ -53,6 +53,7 @@
   "dependencies": {
     "@livekit/components-react": "^2.9.20",
     "@livekit/components-styles": "^1.2.0",
+    "@sentry/electron": "^7.11.0",
     "@tanstack/react-query": "^5.90.21",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",