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/app/api/admin/conversations/route.ts

@@ -0,0 +1,63 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { db } from '@/lib/db';
+import { requireRole } from '@/lib/auth';
+import { getErrorMessage } from '@/lib/errors';
+
+// Admin: Get all conversations
+export async function GET() {
+  try {
+    await requireRole('admin');
+
+    // Get all conversations with participant info and last message
+    const { rows } = await db.query(`
+      SELECT 
+        c.id,
+        c.subject,
+        c.created_at,
+        c.updated_at,
+        (SELECT content FROM direct_messages WHERE conversation_id = c.id ORDER BY created_at DESC LIMIT 1) as last_message,
+        (SELECT created_at FROM direct_messages WHERE conversation_id = c.id ORDER BY created_at DESC LIMIT 1) as last_message_at,
+        (SELECT COUNT(*) FROM direct_messages WHERE conversation_id = c.id) as message_count
+      FROM conversations c
+      ORDER BY c.updated_at DESC
+    `);
+
+    // Get participants for each conversation
+    const conversations = await Promise.all(rows.map(async (conv: any) => {
+      const { rows: participants } = await db.query(`
+        SELECT u.id, u.username, u.first_name, u.last_name, u.role
+        FROM conversation_participants cp
+        JOIN users u ON cp.user_id = u.id
+        WHERE cp.conversation_id = $1
+        ORDER BY u.role DESC, u.first_name
+      `, [conv.id]);
+
+      // Count unread for admins (messages from customers)
+      const { rows: unreadRows } = await db.query(`
+        SELECT COUNT(*) as unread
+        FROM direct_messages dm
+        JOIN users u ON dm.sender_id = u.id
+        WHERE dm.conversation_id = $1
+          AND u.role != 'admin'
+          AND dm.created_at > COALESCE(
+            (SELECT joined_at FROM conversation_participants WHERE conversation_id = $1 AND user_id = (SELECT id FROM users WHERE role = 'admin' LIMIT 1)),
+            '1970-01-01'::timestamp
+          )
+      `, [conv.id]);
+
+      return {
+        ...conv,
+        participants,
+        unread_count: parseInt(unreadRows[0]?.unread || '0')
+      };
+    }));
+
+    return NextResponse.json({ conversations });
+  } catch (error) {
+    console.error('Admin get conversations error:', error);
+    return NextResponse.json(
+      { error: getErrorMessage(error, 'Failed to get conversations') },
+      { status: 500 }
+    );
+  }
+}