feat(sentry): Polish demo page design & fix server instrumentation DSN loading

[HazAT]

What's Changed

Sentry Demo Page Redesign

• Redesigned the Sentry testing page with styling inspired by the official sentry-wizard templates
• Added the official Sentry logo SVG
• Implemented 3D button effects with Sentry's brand colors (#7553FF, #E50045)
• Updated feature cards with inline icons beside headlines for better scannability
• Improved header layout with logo positioned beside the title
• Added clear success/error result states with copyable span.op badges
• Used system-ui font stack for consistent typography
• Added tracesSampleRate & sessionReplay options

Bug Fix

• Fixed instrument.server.mjs crashing when VITE_SENTRY_DSN is not set
• The server instrumentation now gracefully handles missing DSN with a console warning instead of throwing

Screenshots

Before:

After:

🧪 Testing

• Created a TanStack Start app with the Sentry add-on
• Verified error triggering and tracing work correctly
• Confirmed server-side Sentry initialization with DSN