fix: description unreadable in dark mode / OLED — swap disabled textarea for lt-markdown div

Root cause: disabled textarea gets opacity:0.45 + color:var(--text-muted) from
base.css, making it near-invisible on OLED (true-black background).

Fix:
- TicketView: add #ticketDescriptionView (div.lt-markdown) alongside the textarea;
  textarea is now hidden by default (style="display:none"), view div is shown
- ticket.js: renderDescriptionView() renders raw text via parseMarkdown() or nl2br;
  showDescriptionView() / showDescriptionEdit() swap between them;
  toggleEditMode() calls showDescriptionEdit() when entering edit, and
  renderDescriptionView() + showDescriptionView() when returning to read mode
- ticket.css: .ticket-description-view sets full-contrast text-primary/secondary
  colors, min-height, and line-height for comfortable reading

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

views/TicketView.php

@@ -320,12 +320,18 @@ include __DIR__ . '/layout_header.php';
     <div class="lt-section-body">
       <div class="lt-form-group">
         <label class="lt-sr-only lt-label" for="ticketDescription">Description</label>
+        <!-- Read view: shown when not editing — uses lt-markdown for readable typography -->
+        <div id="ticketDescriptionView"
+             class="lt-markdown ticket-description-view"
+             aria-label="Ticket description"></div>
+        <!-- Edit view: shown only when editing -->
         <textarea id="ticketDescription"
                   class="lt-input lt-textarea editable"
                   data-field="description"
                   disabled
                   rows="18"
-                  aria-label="Ticket description"><?= htmlspecialchars($ticket['description'] ?? '') ?></textarea>
+                  style="display:none"
+                  aria-label="Ticket description (edit)"><?= htmlspecialchars($ticket['description'] ?? '') ?></textarea>
       </div>
     </div>
   </div>