feat(crash): comprehensive crash + error reporting for v0.2.3

Adds full-stack crash capture so any unexpected failure — React render,
uncaught JS exception, unhandled promise rejection, or native — is
reported to Sentry with rich, scrubbed context. Expected operational
errors (timeouts, biometric cancel, etc.) stay local to preserve signal.

Changes:
- src/lib/sentry.ts: explicit native crash handlers, release/dist tags
  from app.json, beforeSend/beforeBreadcrumb URL+secret scrubbing,
  addBreadcrumb/captureException helpers, ErrorUtils + onunhandledrejection
  wrappers that always feed the in-memory log buffer (so offline Share
  Report includes the crash too).
- src/components/ErrorBoundary.tsx: new app-wide React boundary with a
  dark recovery screen — error message, top stack/component frames,
  Share Report (clipboard + native share sheet) and Try Again.
- src/lib/diagnostics.ts: buildCrashReport() reuses the existing
  DiagnosticReport pipeline so crashes and connect failures share one
  UI and one transport.
- _layout.tsx: wraps app in ErrorBoundary; emits app.lifecycle
  breadcrumb at startup.
- stores/{connections,events,sessions}.ts: high-signal breadcrumbs at
  connect, SSE connect/disconnect/reconnect, and session select.
- (tabs)/settings.tsx: fix unhandled promise on notificationsGranted().
- app.json: bump expo.version to 0.2.3.
- docs/prd.md, docs/tdd.md: new product + technical design docs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.json

@@ -2,7 +2,7 @@
   "expo": {
     "name": "OpenCode",
     "slug": "opencode-mobile",
-    "version": "0.2.2",
+    "version": "0.2.3",
     "orientation": "portrait",
     "scheme": "opencode",
     "userInterfaceStyle": "automatic",