Fix JS SyntaxError breaking tabs, textarea scrolling, and XSS escaping

Bug fixes:
- ticket.js: Remove duplicate const textarea declaration inside showMentionSuggestions()
  (was redeclaring a parameter, causing SyntaxError that broke all tab switching)
- ticket.css: Add overflow:hidden + resize:none to disabled textarea so description
  shows full height without internal scrollbar (page scrolls instead)
- ticket.js: Trigger height recalculation when entering edit mode on description

XSS/escaping fixes:
- TicketView.php: htmlspecialchars() on description textarea content (closes </textarea> injection risk)
- TicketView.php: htmlspecialchars() on ticket status and workflow transition status strings
- DashboardView.php: htmlspecialchars() on $cat/$type in input value= attributes
- RecurringTicketsView.php: htmlspecialchars() on composed schedule string

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

views/DashboardView.php

@@ -144,7 +144,7 @@ $nonce = SecurityHeadersMiddleware::getNonce();
                         <label>
                             <input type="checkbox"
                                    name="category"
-                                   value="<?php echo $cat; ?>"
+                                   value="<?php echo htmlspecialchars($cat); ?>"
                                    <?php echo in_array($cat, $currentCategories) ? 'checked' : ''; ?>>
                             <?php echo htmlspecialchars($cat); ?>
                         </label>
@@ -161,7 +161,7 @@ $nonce = SecurityHeadersMiddleware::getNonce();
                         <label>
                             <input type="checkbox"
                                    name="type"
-                                   value="<?php echo $type; ?>"
+                                   value="<?php echo htmlspecialchars($type); ?>"
                                    <?php echo in_array($type, $currentTypes) ? 'checked' : ''; ?>>
                             <?php echo htmlspecialchars($type); ?>
                         </label>