Add Ticket Assignment feature (Feature 2)

- Add assigned_to column support in TicketModel with assignTicket() and unassignTicket() methods
- Create assign_ticket.php API endpoint for assignment operations
- Update TicketController to load user list from UserModel
- Add assignment dropdown UI in TicketView
- Add JavaScript handler for assignment changes
- Integrate with audit log for assignment tracking

Users can now assign tickets to team members via dropdown selector.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

api/assign_ticket.php

@@ -0,0 +1,42 @@
+<?php
+session_start();
+require_once '../config/db.php';
+require_once '../models/TicketModel.php';
+require_once '../models/AuditLogModel.php';
+
+header('Content-Type: application/json');
+
+// Check authentication
+if (!isset($_SESSION['user_id'])) {
+    echo json_encode(['success' => false, 'error' => 'Not authenticated']);
+    exit;
+}
+
+// Get request data
+$data = json_decode(file_get_contents('php://input'), true);
+$ticketId = $data['ticket_id'] ?? null;
+$assignedTo = $data['assigned_to'] ?? null;
+
+if (!$ticketId) {
+    echo json_encode(['success' => false, 'error' => 'Ticket ID required']);
+    exit;
+}
+
+$ticketModel = new TicketModel($conn);
+$auditLogModel = new AuditLogModel($conn);
+
+if ($assignedTo === null || $assignedTo === '') {
+    // Unassign ticket
+    $success = $ticketModel->unassignTicket($ticketId, $_SESSION['user_id']);
+    if ($success) {
+        $auditLogModel->log($_SESSION['user_id'], 'unassign', 'ticket', $ticketId);
+    }
+} else {
+    // Assign ticket
+    $success = $ticketModel->assignTicket($ticketId, $assignedTo, $_SESSION['user_id']);
+    if ($success) {
+        $auditLogModel->log($_SESSION['user_id'], 'assign', 'ticket', $ticketId, ['assigned_to' => $assignedTo]);
+    }
+}
+
+echo json_encode(['success' => $success]);