feat: Add 9 new features for enhanced UX and security

Quick Wins:
- Feature 1: Ticket linking in comments (#123456789 auto-links)
- Feature 6: Checkbox click area fix (click anywhere in cell)
- Feature 7: User groups display in settings modal

UI Enhancements:
- Feature 4: Collapsible sidebar with localStorage persistence
- Feature 5: Inline ticket preview popup on hover (300ms delay)
- Feature 2: Mobile responsive improvements (44px touch targets, iOS zoom fix)

Major Features:
- Feature 3: Kanban card view with status columns (toggle with localStorage)
- Feature 9: API key generation admin panel (/admin/api-keys)
- Feature 8: Ticket visibility levels (public/internal/confidential)

New files:
- views/admin/ApiKeysView.php
- api/generate_api_key.php
- api/revoke_api_key.php
- migrations/008_ticket_visibility.sql

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

assets/css/ticket.css

@@ -1499,3 +1499,116 @@ body.dark-mode .editable {
     background: rgba(0, 255, 65, 0.1);
     color: var(--terminal-amber);
 }
+
+/* ===== ENHANCED MOBILE RESPONSIVE - TICKET PAGE ===== */
+@media (max-width: 768px) {
+    /* Prevent iOS zoom on input focus */
+    input[type="text"],
+    input[type="email"],
+    input[type="search"],
+    textarea,
+    select {
+        font-size: 16px !important;
+    }
+
+    /* Touch-friendly button sizes */
+    .btn,
+    button,
+    .tab-btn {
+        min-height: 44px;
+        padding: 12px 16px;
+    }
+
+    /* Stack ticket metadata vertically */
+    .ticket-metadata-fields {
+        grid-template-columns: 1fr !important;
+        gap: 1rem;
+    }
+
+    .metadata-field {
+        width: 100%;
+    }
+
+    /* Stack header controls */
+    .ticket-subheader {
+        flex-direction: column;
+        gap: 1rem;
+    }
+
+    .header-controls {
+        width: 100%;
+        flex-direction: column;
+    }
+
+    .status-priority-group {
+        width: 100%;
+        margin-right: 0;
+    }
+
+    .status-select {
+        width: 100%;
+    }
+
+    /* Full width buttons */
+    #editButton {
+        width: 100%;
+    }
+
+    /* Improve comment form */
+    .comment-form textarea {
+        width: 100%;
+        min-height: 120px;
+    }
+
+    .comment-controls {
+        flex-direction: column;
+        gap: 1rem;
+    }
+
+    .markdown-toggles {
+        flex-direction: column;
+        gap: 0.75rem;
+    }
+
+    /* Improve assignment dropdown */
+    .ticket-assignment {
+        flex-direction: column;
+        align-items: flex-start;
+    }
+
+    .assignment-select {
+        width: 100%;
+        min-height: 44px;
+    }
+
+    /* Full width tabs with better spacing */
+    .ticket-tabs {
+        flex-wrap: wrap;
+    }
+
+    .tab-btn {
+        flex: 1 1 auto;
+        text-align: center;
+        min-width: 100px;
+    }
+
+    /* Improve upload zone */
+    .upload-zone {
+        padding: 1.5rem;
+    }
+
+    .upload-zone-content p {
+        font-size: 0.9rem;
+    }
+
+    /* Improve timeline readability */
+    .timeline-header {
+        flex-direction: column;
+        align-items: flex-start;
+        gap: 0.25rem;
+    }
+
+    .timeline-date {
+        margin-left: 0;
+    }
+}