fix: disable Sentry tracing to prevent CORS failures on Matrix requests

browserTracingIntegration injects sentry-trace and baggage headers into all
outgoing fetch calls. Synapse does not list these in Access-Control-Allow-Headers,
so every Matrix API call was blocked by the browser CORS preflight check.

Removed browserTracingIntegration, set tracePropagationTargets:[] and
tracesSampleRate:0. Error capture (the useful part) is unaffected.
CSP fix (Sentry ingest domain) is applied via nginx — no code change needed.

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

src/index.tsx

@@ -13,13 +13,11 @@ if (sentryDsn) {
     dsn: sentryDsn,
     environment: import.meta.env.MODE,
     release: import.meta.env.VITE_APP_VERSION,
-    integrations: [
-      Sentry.browserTracingIntegration(),
-    ],
-    // Only trace requests to our own Matrix homeserver
-    tracePropagationTargets: ['localhost', /^https:\/\/matrix\.lotusguild\.org/],
-    // 5% of transactions — enough signal without burning quota
-    tracesSampleRate: 0.05,
+    // 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