Implement comprehensive improvement plan (Phases 1-6)

Security (Phase 1-2):
- Add SecurityHeadersMiddleware with CSP, X-Frame-Options, etc.
- Add RateLimitMiddleware for API rate limiting
- Add security event logging to AuditLogModel
- Add ResponseHelper for standardized API responses
- Update config.php with security constants

Database (Phase 3):
- Add migration 014 for additional indexes
- Add migration 015 for ticket dependencies
- Add migration 016 for ticket attachments
- Add migration 017 for recurring tickets
- Add migration 018 for custom fields

Features (Phase 4-5):
- Add ticket dependencies with DependencyModel and API
- Add duplicate detection with check_duplicates API
- Add file attachments with AttachmentModel and upload/download APIs
- Add @mentions with autocomplete and highlighting
- Add quick actions on dashboard rows

Collaboration (Phase 5):
- Add mention extraction in CommentModel
- Add mention autocomplete dropdown in ticket.js
- Add mention highlighting CSS styles

Admin & Export (Phase 6):
- Add StatsModel for dashboard widgets
- Add dashboard stats cards (open, critical, unassigned, etc.)
- Add CSV/JSON export via export_tickets API
- Add rich text editor toolbar in markdown.js
- Add RecurringTicketModel with cron job
- Add CustomFieldModel for per-category fields
- Add admin views: RecurringTickets, CustomFields, Workflow,
  Templates, AuditLog, UserActivity
- Add admin APIs: manage_workflows, manage_templates,
  manage_recurring, custom_fields, get_users
- Add admin routes in index.php

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

assets/css/dashboard.css

@@ -3000,3 +3000,169 @@ code.inline-code {
     margin-top: 0.25rem;
     font-style: italic;
 }
+
+/* ===== QUICK ACTIONS ===== */
+.quick-actions-cell {
+    text-align: center;
+    white-space: nowrap;
+}
+
+.quick-actions {
+    display: flex;
+    gap: 0.25rem;
+    justify-content: center;
+    opacity: 0.5;
+    transition: opacity 0.2s ease;
+}
+
+tr:hover .quick-actions {
+    opacity: 1;
+}
+
+.quick-action-btn {
+    background: transparent;
+    border: 1px solid var(--terminal-green);
+    color: var(--terminal-green);
+    padding: 0.25rem 0.5rem;
+    font-size: 0.9rem;
+    cursor: pointer;
+    transition: all 0.2s ease;
+    border-radius: 0;
+}
+
+.quick-action-btn:hover {
+    background: var(--terminal-green);
+    color: var(--bg-primary);
+    box-shadow: var(--glow-green);
+}
+
+/* ===== DASHBOARD STATS WIDGETS ===== */
+.stats-widgets {
+    margin-bottom: 1.5rem;
+}
+
+.stats-row {
+    display: grid;
+    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
+    gap: 1rem;
+}
+
+.stat-card {
+    display: flex;
+    align-items: center;
+    gap: 0.75rem;
+    padding: 1rem;
+    background: var(--bg-secondary);
+    border: 2px solid var(--terminal-green);
+    transition: all 0.3s ease;
+}
+
+.stat-card:hover {
+    border-color: var(--terminal-amber);
+    box-shadow: var(--glow-amber);
+}
+
+.stat-icon {
+    font-size: 1.5rem;
+    opacity: 0.9;
+}
+
+.stat-content {
+    flex: 1;
+}
+
+.stat-value {
+    font-size: 1.5rem;
+    font-weight: bold;
+    color: var(--terminal-green);
+    line-height: 1;
+    text-shadow: var(--glow-green);
+}
+
+.stat-label {
+    font-size: 0.8rem;
+    color: var(--terminal-green-dim, #008822);
+    margin-top: 0.25rem;
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+}
+
+/* Stat card color variations */
+.stat-critical .stat-value {
+    color: var(--priority-1);
+    text-shadow: var(--glow-red);
+}
+
+.stat-critical {
+    border-color: var(--priority-1);
+}
+
+.stat-unassigned .stat-value {
+    color: var(--terminal-amber);
+    text-shadow: var(--glow-amber);
+}
+
+.stat-unassigned {
+    border-color: var(--terminal-amber);
+}
+
+/* Mobile responsive stats */
+@media (max-width: 768px) {
+    .stats-row {
+        grid-template-columns: repeat(2, 1fr);
+    }
+
+    .stat-card {
+        padding: 0.75rem;
+    }
+
+    .stat-value {
+        font-size: 1.25rem;
+    }
+
+    .stat-icon {
+        font-size: 1.25rem;
+    }
+}
+
+@media (max-width: 480px) {
+    .stats-row {
+        grid-template-columns: 1fr;
+    }
+}
+
+/* ===== EXPORT DROPDOWN ===== */
+.export-dropdown {
+    position: relative;
+    display: inline-block;
+}
+
+.export-dropdown-content {
+    display: none;
+    position: absolute;
+    top: 100%;
+    right: 0;
+    background: var(--bg-primary);
+    border: 2px solid var(--terminal-green);
+    min-width: 120px;
+    z-index: 100;
+    box-shadow: 0 0 10px rgba(0, 255, 65, 0.3);
+}
+
+.export-dropdown:hover .export-dropdown-content {
+    display: block;
+}
+
+.export-dropdown-content a {
+    display: block;
+    padding: 0.5rem 1rem;
+    color: var(--terminal-green);
+    text-decoration: none;
+    font-family: var(--font-mono);
+    transition: all 0.2s ease;
+}
+
+.export-dropdown-content a:hover {
+    background: rgba(0, 255, 65, 0.1);
+    color: var(--terminal-amber);
+}