chore: remove Sentry integration

Remove @sentry/nextjs and all related files since it was never actively used.
- Delete sentry.server.config.ts, sentry.edge.config.ts
- Delete sentry-example-page and sentry-example-api routes
- Clean up instrumentation.ts, global-error.tsx, middleware.ts
- Remove Sentry env vars from env.example and docs
- Update CLAUDE.md, copilot-instructions.md, PRODUCTION_READINESS.md

Middleware bundle reduced from 86KB to 34.8KB (-51KB).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

CLAUDE.md

@@ -16,7 +16,7 @@ Personal portfolio website for Dennis Konkol (dk0.dev). Built with Next.js 15 (A
 - **CMS**: Directus (self-hosted, REST/GraphQL, optional)
 - **Automation**: n8n webhooks (status, chat, hardcover, image generation)
 - **i18n**: next-intl (EN + DE), message files in `messages/`
-- **Monitoring**: Sentry
+- **Monitoring**: Console error logging (development mode only)
 - **Deployment**: Docker + Nginx, CI via Gitea Actions
 
 ## Commands
@@ -122,7 +122,6 @@ DATABASE_URL=postgresql://...
 
 # Optional
 REDIS_URL=redis://...
-SENTRY_DSN=...
 ```
 
 ## Conventions