Add comprehensive accessibility improvements

HTML Accessibility:
- Add ARIA roles to tab navigation (role="tablist", role="tab", role="tabpanel")
- Add aria-selected to tab buttons with JS toggle
- Add aria-controls and aria-labelledby for tab/panel relationships
- Add aria-label to emoji icon buttons (settings, reply, edit, delete)
- Add aria-pressed to view toggle buttons
- Add labels for form inputs (comment textarea, dependency inputs, file input)
- Add .sr-only utility class for screen-reader-only content

CSS Accessibility:
- Add .sr-only class (visually hidden, accessible to screen readers)

JavaScript:
- Update showTab() to toggle aria-selected on tab buttons

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

views/DashboardView.php

@@ -96,7 +96,7 @@ $nonce = SecurityHeadersMiddleware::getNonce();
                         </div>
                     </div>
                 <?php endif; ?>
-                <button class="settings-icon" title="Settings (Alt+S)" data-action="open-settings">⚙</button>
+                <button class="settings-icon" title="Settings (Alt+S)" data-action="open-settings" aria-label="Settings">⚙</button>
             <?php endif; ?>
         </div>
     </div>
@@ -284,8 +284,8 @@ $nonce = SecurityHeadersMiddleware::getNonce();
         <!-- Center: Actions + Count -->
         <div class="toolbar-center">
             <div class="view-toggle">
-                <button id="tableViewBtn" class="view-btn active" data-action="set-view-mode" data-mode="table" title="Table View">≡</button>
-                <button id="cardViewBtn" class="view-btn" data-action="set-view-mode" data-mode="card" title="Kanban View">▦</button>
+                <button id="tableViewBtn" class="view-btn active" data-action="set-view-mode" data-mode="table" title="Table View" aria-label="Table view" aria-pressed="true">≡</button>
+                <button id="cardViewBtn" class="view-btn" data-action="set-view-mode" data-mode="card" title="Kanban View" aria-label="Kanban view" aria-pressed="false">▦</button>
             </div>
             <button data-action="navigate" data-url="<?php echo $GLOBALS['config']['BASE_URL']; ?>/ticket/create" class="btn create-ticket">+ New Ticket</button>
             <div class="export-dropdown" id="exportDropdown" style="display: none;">