fix: Resolve multiple UI and API bugs

- Remove is_active filter from get_users.php (column doesn't exist)
- Fix ticket ID validation regex in upload_attachment.php (9-digit format)
- Fix createSettingsModal reference to use openSettingsModal from settings.js
- Add error handling for dependencies tab to prevent infinite loading
- Add try-catch wrapper to ticket_dependencies.php API
- Make export dropdown visible only when tickets are selected
- Export only selected tickets instead of all filtered tickets

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

assets/js/ticket.js

@@ -579,20 +579,39 @@ function loadDependencies() {
     const ticketId = window.ticketData.id;
 
     fetch(`/api/ticket_dependencies.php?ticket_id=${ticketId}`)
-        .then(response => response.json())
+        .then(response => {
+            if (!response.ok) {
+                throw new Error(`HTTP ${response.status}`);
+            }
+            return response.json();
+        })
         .then(data => {
             if (data.success) {
                 renderDependencies(data.dependencies);
                 renderDependents(data.dependents);
             } else {
                 console.error('Error loading dependencies:', data.error);
+                showDependencyError(data.error || 'Failed to load dependencies');
             }
         })
         .catch(error => {
             console.error('Error loading dependencies:', error);
+            showDependencyError('Failed to load dependencies. The feature may not be available.');
         });
 }
 
+function showDependencyError(message) {
+    const dependenciesList = document.getElementById('dependenciesList');
+    const dependentsList = document.getElementById('dependentsList');
+
+    if (dependenciesList) {
+        dependenciesList.innerHTML = `<p style="color: var(--terminal-amber);">${escapeHtml(message)}</p>`;
+    }
+    if (dependentsList) {
+        dependentsList.innerHTML = `<p style="color: var(--terminal-amber);">${escapeHtml(message)}</p>`;
+    }
+}
+
 function renderDependencies(dependencies) {
     const container = document.getElementById('dependenciesList');
     if (!container) return;