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/streams.js

@@ -26,7 +26,7 @@ import {
 import { API_BASE, getHeaders, fetchWithAuth, escapeHtml } from '../core/api.js';
 import { t } from '../core/i18n.js';
 import { Modal } from '../core/modal.js';
-import { showToast, showConfirm, openLightbox, openFullImageLightbox, showOverlaySpinner, hideOverlaySpinner } from '../core/ui.js';
+import { showToast, showConfirm, openLightbox, openFullImageLightbox, showOverlaySpinner, hideOverlaySpinner, setTabRefreshing } from '../core/ui.js';
 import { openDisplayPicker, formatDisplayLabel } from './displays.js';
 import { CardSection } from '../core/card-sections.js';
 import { updateSubTabHash } from './tabs.js';
@@ -516,6 +516,7 @@ export async function deleteTemplate(templateId) {
 export async function loadPictureSources() {
     if (_sourcesLoading) return;
     set_sourcesLoading(true);
+    setTabRefreshing('streams-list', true);
     try {
         const [filtersResp, ppResp, captResp, streamsResp, audioResp, valueResp] = await Promise.all([
             _availableFilters.length === 0 ? fetchWithAuth('/filters') : Promise.resolve(null),
@@ -558,6 +559,7 @@ export async function loadPictureSources() {
         `;
     } finally {
         set_sourcesLoading(false);
+        setTabRefreshing('streams-list', false);
     }
 }