Fix dark mode bulk toolbar, light mode timeline, and activity tab visibility

- Changed bulk-actions-toolbar dark mode background from #1a1a00 to #2d3748
- Fixed timeline-content light mode background from #1a202c to #f8f9fa
- Added activity-tab to showTab() function to properly hide/show all tabs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

assets/css/ticket.css

@@ -478,7 +478,7 @@ input:checked + .slider:before {
 
 .timeline-content {
     flex: 1;
-    background: var(--card-bg, #1a202c);
+    background: var(--card-bg, #f8f9fa);
     padding: 0.75rem 1rem;
     border-radius: 8px;
     border: 1px solid var(--border-color, #ddd);