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/dashboard.js

@@ -5,7 +5,7 @@
 import { apiKey, _dashboardLoading, set_dashboardLoading, dashboardPollInterval, setDashboardPollInterval } from '../core/state.js';
 import { API_BASE, getHeaders, fetchWithAuth, escapeHtml } from '../core/api.js';
 import { t } from '../core/i18n.js';
-import { showToast, formatUptime } from '../core/ui.js';
+import { showToast, formatUptime, setTabRefreshing } from '../core/ui.js';
 import { renderPerfSection, initPerfCharts, startPerfPolling, stopPerfPolling } from './perf-charts.js';
 import { startAutoRefresh, updateTabBadge } from './tabs.js';
 import {
@@ -302,6 +302,7 @@ export async function loadDashboard(forceFullRender = false) {
     set_dashboardLoading(true);
     const container = document.getElementById('dashboard-content');
     if (!container) { set_dashboardLoading(false); return; }
+    setTabRefreshing('dashboard-content', true);
 
     try {
         const [targetsResp, profilesResp, devicesResp, cssResp] = await Promise.all([
@@ -481,6 +482,7 @@ export async function loadDashboard(forceFullRender = false) {
         container.innerHTML = `<div class="dashboard-no-targets">${t('dashboard.failed')}</div>`;
     } finally {
         set_dashboardLoading(false);
+        setTabRefreshing('dashboard-content', false);
     }
 }