refactor(observability): lower trace sample rate, add DSN comment, improve status visibility

- Lower tracesSampleRate from 1.0 to 0.1 in both hooks (errors still captured
  at 100%; trace volume reduced for self-hosted GlitchTip on shared VPS)
- Add comment explaining VITE_SENTRY_DSN is a write-only ingest key, safe in
  client bundle — prevents accidental rotation as if it were a password
- Restore HTTP status code prominence: text-4xl font-bold (was text-xs text-ink-3)
- Add min-w-[44px] to copy button for WCAG 2.2 minimum touch target

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

frontend/src/hooks.client.ts

@@ -1,9 +1,11 @@
 import * as Sentry from '@sentry/sveltekit';
 
+// VITE_SENTRY_DSN is a write-only ingest key — it can POST events to GlitchTip
+// but cannot read them. Safe to include in the client bundle per Sentry security model.
 Sentry.init({
 	dsn: import.meta.env.VITE_SENTRY_DSN,
 	environment: import.meta.env.MODE,
-	tracesSampleRate: 1.0,
+	tracesSampleRate: 0.1,
 	sendDefaultPii: false,
 	enabled: !!import.meta.env.VITE_SENTRY_DSN
 });