Frontend: structured error handling, state fixes, accessibility, i18n

- Enhance fetchWithAuth with auto-401, retry w/ exponential backoff, timeout
- Remove ~40 manual 401 checks across 10 feature files
- Fix state: brightness cache setter, manual edit flag resets, static import
- Add ARIA: role=dialog/tablist, aria-modal, aria-labelledby, aria-selected
- Add focus trapping in Modal base class, aria-expanded on hint toggles
- Fix WCAG AA color contrast with --primary-text-color variable
- Add i18n pluralization (CLDR rules for en/ru), getCurrentLocale export
- Replace hardcoded strings in dashboard.js and profiles.js
- Add data-i18n-aria-label support, 20 new keys in en.json and ru.json

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

server/src/wled_controller/static/js/features/calibration.js

@@ -5,7 +5,7 @@
 import {
     calibrationTestState, EDGE_TEST_COLORS,
 } from '../core/state.js';
-import { API_BASE, getHeaders, handle401Error } from '../core/api.js';
+import { API_BASE, getHeaders, fetchWithAuth } from '../core/api.js';
 import { showToast } from '../core/ui.js';
 import { Modal } from '../core/modal.js';
 import { closeTutorial, startCalibrationTutorial } from './tutorials.js';
@@ -53,11 +53,10 @@ let _previewRaf = null;
 export async function showCalibration(deviceId) {
     try {
         const [response, displaysResponse] = await Promise.all([
-            fetch(`${API_BASE}/devices/${deviceId}`, { headers: getHeaders() }),
-            fetch(`${API_BASE}/config/displays`, { headers: getHeaders() }),
+            fetchWithAuth(`/devices/${deviceId}`),
+            fetchWithAuth('/config/displays'),
         ]);
 
-        if (response.status === 401) { handle401Error(); return; }
         if (!response.ok) { showToast('Failed to load calibration', 'error'); return; }
 
         const device = await response.json();
@@ -131,6 +130,7 @@ export async function showCalibration(deviceId) {
         window._calibrationResizeObserver.observe(preview);
 
     } catch (error) {
+        if (error.isAuth) return;
         console.error('Failed to load calibration:', error);
         showToast('Failed to load calibration', 'error');
     }
@@ -626,18 +626,17 @@ export async function toggleTestEdge(edge) {
     updateCalibrationPreview();
 
     try {
-        const response = await fetch(`${API_BASE}/devices/${deviceId}/calibration/test`, {
+        const response = await fetchWithAuth(`/devices/${deviceId}/calibration/test`, {
             method: 'PUT',
-            headers: getHeaders(),
             body: JSON.stringify({ edges })
         });
-        if (response.status === 401) { handle401Error(); return; }
         if (!response.ok) {
             const errorData = await response.json();
             error.textContent = `Test failed: ${errorData.detail}`;
             error.style.display = 'block';
         }
     } catch (err) {
+        if (err.isAuth) return;
         console.error('Failed to toggle test edge:', err);
         error.textContent = 'Failed to toggle test edge';
         error.style.display = 'block';
@@ -696,12 +695,10 @@ export async function saveCalibration() {
     };
 
     try {
-        const response = await fetch(`${API_BASE}/devices/${deviceId}/calibration`, {
+        const response = await fetchWithAuth(`/devices/${deviceId}/calibration`, {
             method: 'PUT',
-            headers: getHeaders(),
             body: JSON.stringify(calibration)
         });
-        if (response.status === 401) { handle401Error(); return; }
         if (response.ok) {
             showToast('Calibration saved', 'success');
             calibModal.forceClose();
@@ -712,6 +709,7 @@ export async function saveCalibration() {
             error.style.display = 'block';
         }
     } catch (err) {
+        if (err.isAuth) return;
         console.error('Failed to save calibration:', err);
         error.textContent = 'Failed to save calibration';
         error.style.display = 'block';