Frontend polish: loading states, CSS variables, focus indicators, scroll lock

- Add tab refresh loading bar animation for all 4 tab loaders
- Add profiles loading guard to prevent concurrent fetches
- Centralize theme colors into CSS variables (--text-secondary, --text-muted,
  --bg-secondary, --success-color, --shadow-color) for both dark/light themes
- Replace hardcoded gray values across 10 CSS files with variables
- Fix duplicate .btn-sm definition in modal.css
- Fix z-index: toast 2001→2500 to safely clear modals at 2000
- Add :focus-visible keyboard navigation indicators for all interactive elements
- Add responsive breakpoints for tab bar and header on narrow screens
- Prevent background page scroll when command palette is open

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

server/src/wled_controller/static/css/patterns.css

@@ -25,10 +25,10 @@
     border-radius: 4px;
 }
 .validation-status.success {
-    color: #4caf50;
+    color: var(--primary-color);
 }
 .validation-status.error {
-    color: #f44336;
+    color: var(--danger-color);
 }
 .validation-status.loading {
     color: var(--text-muted);
@@ -131,7 +131,7 @@
 .kc-rect-row .kc-rect-remove-btn {
     background: none;
     border: none;
-    color: #777;
+    color: var(--text-muted);
     font-size: 1rem;
     cursor: pointer;
     padding: 4px;
@@ -336,7 +336,7 @@
 .pattern-rect-row .pattern-rect-remove-btn {
     background: none;
     border: none;
-    color: #777;
+    color: var(--text-muted);
     font-size: 0.9rem;
     cursor: pointer;
     padding: 2px 4px;