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>

assets/js/ticket.js

@@ -213,7 +213,7 @@ function toggleMarkdownMode() {
 document.addEventListener('DOMContentLoaded', function() {
     // Show description tab by default
     showTab('description');
-    
+
     // Auto-resize the description textarea to fit content
     const descriptionTextarea = document.querySelector('textarea[data-field="description"]');
     if (descriptionTextarea) {
@@ -223,15 +223,50 @@ document.addEventListener('DOMContentLoaded', function() {
             // Set the height to match the scrollHeight
             descriptionTextarea.style.height = descriptionTextarea.scrollHeight + 'px';
         }
-        
+
         // Initial resize
         autoResizeTextarea();
-        
+
         // Resize on input when in edit mode
         descriptionTextarea.addEventListener('input', autoResizeTextarea);
     }
+
+    // Initialize assignment handling
+    handleAssignmentChange();
 });
 
+/**
+ * Handle ticket assignment dropdown changes
+ */
+function handleAssignmentChange() {
+    const assignedToSelect = document.getElementById('assignedToSelect');
+    if (!assignedToSelect) return;
+
+    assignedToSelect.addEventListener('change', function() {
+        const ticketId = window.ticketData.id;
+        const assignedTo = this.value || null;
+
+        fetch('/api/assign_ticket.php', {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({ ticket_id: ticketId, assigned_to: assignedTo })
+        })
+        .then(response => response.json())
+        .then(data => {
+            if (!data.success) {
+                alert('Error updating assignment');
+                console.error(data.error);
+            } else {
+                console.log('Assignment updated successfully');
+            }
+        })
+        .catch(error => {
+            console.error('Error updating assignment:', error);
+            alert('Error updating assignment: ' + error.message);
+        });
+    });
+}
+
 function showTab(tabName) {
     // Hide all tab contents
     const descriptionTab = document.getElementById('description-tab');