Adds @sentry/sveltekit to hooks.client.ts and hooks.server.ts.
When VITE_SENTRY_DSN is unset (default), Sentry is fully disabled.
When set to a GlitchTip JavaScript project DSN, browser exceptions
and SSR handleError events are forwarded automatically.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
