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>

pnpm-workspace.yaml

@@ -6,6 +6,7 @@ packages:
   - 'memoro'
   - 'picture'
   - 'uload'
+  - 'chat'
 
   # Sub-apps within projects
   - 'maerchenzauber/apps/*'
@@ -17,6 +18,9 @@ packages:
   - 'picture/apps/*'
   - 'picture/packages/*'
   - 'uload/apps/*'
+  - 'chat/apps/*'
+  - 'chat/backend'
+  - 'chat/packages/*'
 
   # Shared packages
   - 'packages/*'