chore: remove Sentry.io entirely

We no longer use Sentry. Removed:
- @sentry/react + @sentry/vite-plugin (package.json + lockfile)
- Sentry.init in index.tsx and the VITE_SENTRY_DSN env (.env.production)
- @sentry/vite-plugin + the SENTRY_AUTH_TOKEN sourcemap-upload path in
  vite.config.js (sourcemap now always false) and the CI env var
- Sentry.ErrorBoundary in App.tsx -> react-error-boundary's ErrorBoundary with a
  folds-native fallback (Box/Text/Button + config tokens), which also resolves
  the native-cinny audit's raw-#hex/#5865f2 fallback finding.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/index.tsx

@@ -1,5 +1,4 @@
 /* eslint-disable import/first */
-import * as Sentry from '@sentry/react';
 import React from 'react';
 import { createRoot } from 'react-dom/client';
 import { enableMapSet } from 'immer';
@@ -7,31 +6,6 @@ import '@fontsource-variable/inter/index.css';
 import 'folds/dist/style.css';
 import { configClass, varsClass } from 'folds';
 
-const sentryDsn = import.meta.env.VITE_SENTRY_DSN;
-if (sentryDsn) {
-  Sentry.init({
-    dsn: sentryDsn,
-    environment: import.meta.env.MODE,
-    release: import.meta.env.VITE_APP_VERSION,
-    // browserTracingIntegration omitted — it injects sentry-trace/baggage headers
-    // into outgoing fetch calls, which breaks Synapse CORS on matrix.lotusguild.org
-    // No propagation targets — we don't control the Matrix server's CORS allow-list
-    tracePropagationTargets: [],
-    tracesSampleRate: 0,
-    // Don't send PII (IPs, usernames) — this is a private chat app
-    sendDefaultPii: false,
-    // Forward Sentry logs to the dashboard
-    enableLogs: true,
-    // Suppress benign PostmessageTransport / matrixRTC heartbeat timeouts (upstream library noise)
-    ignoreErrors: ['Request timed out'],
-    beforeSend(event) {
-      // Drop any event that may have leaked an access token into breadcrumbs/data
-      if (JSON.stringify(event).includes('access_token')) return null;
-      return event;
-    },
-  });
-}
-
 enableMapSet();
 
 import './index.css';