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/scripts/add_conversation_title.sql

@@ -0,0 +1,19 @@
+-- SQL zum Hinzufügen der Titel-Spalte zur Conversations-Tabelle
+-- SCHRITT 1: Spalte zur Tabelle hinzufügen
+ALTER TABLE conversations
+ADD COLUMN IF NOT EXISTS title TEXT;
+
+-- SCHRITT 2: Kommentar für Dokumentation hinzufügen
+COMMENT ON COLUMN conversations.title IS 'KI-generierter Titel für die Konversation';
+
+-- SCHRITT 3: Aktualisiere RLS-Policy (Row Level Security) für die neue Spalte
+-- (Stelle sicher, dass Benutzer nur ihre eigenen Konversationen lesen/bearbeiten können)
+DROP POLICY IF EXISTS "Users can update their own conversations" ON conversations;
+CREATE POLICY "Users can update their own conversations" 
+ON conversations
+FOR UPDATE USING (user_id = auth.uid());
+
+-- SCHRITT 4: (Optional) Standardwerte für bestehende Konversationen setzen
+UPDATE conversations
+SET title = 'Frühere Konversation'
+WHERE title IS NULL;