feat(chat): integrate chat project into monorepo with full app structure

- Restructure chat as apps/mobile, apps/web, apps/landing, backend
- Add NestJS backend for secure Azure OpenAI API calls
- Remove exposed API key from mobile app (security fix)
- Add shared chat-types package
- Create SvelteKit web app scaffold
- Create Astro landing page scaffold
- Update pnpm workspace configuration
- Add project-level CLAUDE.md documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

chat/apps/mobile/.env.example

@@ -0,0 +1,7 @@
+# Supabase Konfiguration
+EXPO_PUBLIC_SUPABASE_URL=https://your-project.supabase.co
+EXPO_PUBLIC_SUPABASE_ANON_KEY=your-supabase-anon-key
+
+# Chat Backend API
+# The backend handles AI API calls securely - no API keys needed in the mobile app
+EXPO_PUBLIC_BACKEND_URL=http://localhost:3001