feat: add messaging system with admin bulk messages and user conversations

- Add conversations and direct_messages tables to schema
- User messaging page at /messages (users can start conversations, see admin responses)
- Admin messaging page at /admin/messages (view all conversations, reply to users)
- Admin bulk messaging: send to all customers, specific users, or admins
- Mail icon in navbar for logged-in users (links to appropriate messaging page)
- Show first name of admin who responded in conversation view
- Clean build cache after middleware changes

package.json

@@ -13,7 +13,7 @@
     "@chenglou/pretext": "^0.0.8",
     "bcryptjs": "^2.4.3",
     "jose": "^5.6.3",
-    "next": "14.2.28",
+    "next": "^14.2.35",
     "pg": "^8.12.0",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",