Fix close-ticket UX, add cmd palette hint, breadcrumb, image lightbox

- ticket.js: status change requiring a comment now shows an inline
  modal with a textarea — comment is actually posted before the status
  changes, instead of just warning the user and changing anyway
- layout_header.php: add ⌘K button in header so users can discover
  the command palette; also removes inline onclick in favor of JS
  (CSP-safe via nonce script block already present)
- TicketView.php: upgrade breadcrumb to lt-breadcrumb markup with
  ticket title preview (truncated at 45 chars) and aria-current
- ticket.js + ticket.css: image attachments now render as clickable
  thumbnails (3rem×3rem) that open in lt.lightbox; non-image files
  keep the icon display unchanged

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

views/layout_header.php

@@ -200,6 +200,12 @@ $_lt_assetVer  = $GLOBALS['config']['ASSET_VERSION'] ?? '20260329';
         </div>
       </div>
 <?php endif; ?>
+      <button type="button" id="lt-cmd-trigger"
+              class="lt-btn lt-btn-ghost lt-btn-sm"
+              title="Command palette (Ctrl+K)"
+              aria-label="Open command palette"
+              onclick="if(window.lt&&lt.cmdPalette)lt.cmdPalette.open()"
+              style="font-size:0.65rem;opacity:0.65;letter-spacing:0.03em;padding:0.2rem 0.45rem">&#x2315;&nbsp;K</button>
       <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 -->