Align UI with web_template TDS v1.2 standards

- Replace lt-chip priority badges with lt-badge lt-badge-p[1-4] across
  DashboardView, TemplatesView (matches web_template sticky table pattern)
- Add lt-theme-btn theme toggle to header-right; wire lt.theme.toggle()
- Replace ASCII art empty state with lt-empty-state component in dashboard
- Standardize tab wrapper lt-tabs → lt-tab-bar in Dashboard and TicketView
- Add missing lt-keys-help modal to layout_footer (fixes ? key doing nothing)
- Add lt-cmd-overlay command palette container + lt.cmdPalette.init() nav
- Add .lt-timeline-action CSS rule (used in TicketView, was undefined)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

views/layout_header.php

@@ -156,6 +156,8 @@ $_lt_navActive = $activeNav ?? 'dashboard';
       <span class="lt-badge lt-badge-admin" aria-label="Administrator">ADMIN</span>
 <?php   endif; ?>
 <?php endif; ?>
+      <button type="button" class="lt-theme-btn" id="lt-theme-btn"
+              aria-label="Switch to light mode" title="Switch to light mode">&#x2600;</button>
     </div><!-- /.lt-header-right -->
 
   </header><!-- /.lt-header -->