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/fix_models_table.sql

@@ -0,0 +1,27 @@
+-- Überprüfe die aktuelle Struktur der models-Tabelle
+SELECT column_name, data_type 
+FROM information_schema.columns 
+WHERE table_name = 'models';
+
+-- Füge die fehlenden Spalten hinzu, wenn sie nicht existieren
+DO $$
+BEGIN
+    -- Überprüfe, ob created_at existiert
+    IF NOT EXISTS (
+        SELECT 1
+        FROM information_schema.columns
+        WHERE table_name = 'models' AND column_name = 'created_at'
+    ) THEN
+        ALTER TABLE models ADD COLUMN created_at TIMESTAMPTZ DEFAULT now();
+    END IF;
+
+    -- Überprüfe, ob updated_at existiert
+    IF NOT EXISTS (
+        SELECT 1
+        FROM information_schema.columns
+        WHERE table_name = 'models' AND column_name = 'updated_at'
+    ) THEN
+        ALTER TABLE models ADD COLUMN updated_at TIMESTAMPTZ DEFAULT now();
+    END IF;
+END
+$$;