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/js/features/targets.js

@@ -12,7 +12,7 @@ import {
 } from '../core/state.js';
 import { API_BASE, getHeaders, fetchWithAuth, escapeHtml } from '../core/api.js';
 import { t } from '../core/i18n.js';
-import { showToast, showConfirm, formatUptime } from '../core/ui.js';
+import { showToast, showConfirm, formatUptime, setTabRefreshing } from '../core/ui.js';
 import { Modal } from '../core/modal.js';
 import { createDeviceCard, attachDeviceListeners, fetchDeviceBrightness, _computeMaxFps } from './devices.js';
 import { createKCTargetCard, connectKCWebSocket, disconnectKCWebSocket } from './kc-targets.js';
@@ -407,6 +407,7 @@ export async function loadTargetsTab() {
     // Skip if another loadTargetsTab or a button action is already running
     if (_loadTargetsLock || _actionInFlight) return;
     _loadTargetsLock = true;
+    setTabRefreshing('targets-panel-content', true);
 
     try {
         // Fetch devices, targets, CSS sources, picture sources, pattern templates, and value sources in parallel
@@ -654,6 +655,7 @@ export async function loadTargetsTab() {
         container.innerHTML = `<div class="loading">${t('targets.failed')}</div>`;
     } finally {
         _loadTargetsLock = false;
+        setTabRefreshing('targets-panel-content', false);
     }
 }