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

src/lib/auth.ts

@@ -54,9 +54,9 @@ export async function authenticateUser(username: string, password: string) {
 export async function createSession(user: { id: number; username: string; role: string }) {
   const token = await new SignJWT({ id: user.id, username: user.username, role: user.role })
     .setProtectedHeader({ alg: 'HS256' })
-    .setExpirationTime('7d')
+    .setExpirationTime('4h') // 4 hours for security (reduced from 7 days)
     .sign(getSecret());
-  cookies().set('session', token, { httpOnly: true, secure: process.env.NODE_ENV === 'production', sameSite: 'lax', maxAge: 60 * 60 * 24 * 7 });
+  cookies().set('session', token, { httpOnly: true, secure: process.env.NODE_ENV === 'production', sameSite: 'lax', maxAge: 60 * 60 * 4 }); // 4 hours
   return token;
 }