Frontend improvements: CSS foundations, accessibility, UX enhancements

CSS: Add design token variables (spacing, timing, weights, z-index layers),
migrate all hardcoded z-index to named vars, fix light theme contrast for
WCAG AA, add skeleton loading cards, mask-composite fallback, card padding.

Accessibility: aria-live on toast, aria-label on health dots, sr-only class,
graph container keyboard focusable, MQTT password wrapped in form element.

UX: Modal auto-focus on open, inline field validation with blur, undo toast
with countdown, bulk action progress indicator, API error toast on failure.

i18n: Add common.undo, validation.required, bulk.processing, api.error.*
keys in EN/RU/ZH.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/wled_controller/static/js/app.ts

@@ -18,8 +18,9 @@ import { initTabIndicator, updateTabIndicator } from './core/tab-indicator.ts';
 // Layer 2: ui
 import {
     toggleHint, lockBody, unlockBody, closeLightbox,
-    showToast, showConfirm, closeConfirmModal,
+    showToast, showUndoToast, showConfirm, closeConfirmModal,
     openFullImageLightbox, showOverlaySpinner, hideOverlaySpinner,
+    setFieldError, clearFieldError, setupBlurValidation,
 } from './core/ui.ts';
 
 // Layer 3: displays, tutorials
@@ -86,7 +87,7 @@ import {
     clonePatternTemplate,
 } from './features/pattern-templates.ts';
 import {
-    loadAutomations, openAutomationEditor, closeAutomationEditorModal,
+    loadAutomations, switchAutomationTab, openAutomationEditor, closeAutomationEditorModal,
     saveAutomationEditor, addAutomationCondition,
     toggleAutomationEnabled, cloneAutomation, deleteAutomation, copyWebhookUrl,
 } from './features/automations.ts';
@@ -208,11 +209,15 @@ Object.assign(window, {
     unlockBody,
     closeLightbox,
     showToast,
+    showUndoToast,
     showConfirm,
     closeConfirmModal,
     openFullImageLightbox,
     showOverlaySpinner,
     hideOverlaySpinner,
+    setFieldError,
+    clearFieldError,
+    setupBlurValidation,
 
     // core / api + i18n
     t,
@@ -365,6 +370,7 @@ Object.assign(window, {
 
     // automations
     loadAutomations,
+    switchAutomationTab,
     openAutomationEditor,
     closeAutomationEditorModal,
     saveAutomationEditor,