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/locales/en.json

@@ -512,5 +512,24 @@
   "profiles.status.active": "Active",
   "profiles.status.inactive": "Inactive",
   "profiles.status.disabled": "Disabled",
-  "profiles.last_activated": "Last activated"
+  "profiles.last_activated": "Last activated",
+  "profiles.logic.and": " AND ",
+  "profiles.logic.or": " OR ",
+  "profiles.logic.all": "ALL",
+  "profiles.logic.any": "ANY",
+  "profiles.updated": "Profile updated",
+  "profiles.created": "Profile created",
+  "profiles.deleted": "Profile deleted",
+  "profiles.error.name_required": "Name is required",
+  "time.hours_minutes": "{h}h {m}m",
+  "time.minutes_seconds": "{m}m {s}s",
+  "time.seconds": "{s}s",
+  "dashboard.type.led": "LED",
+  "dashboard.type.kc": "Key Colors",
+  "aria.close": "Close",
+  "aria.save": "Save",
+  "aria.cancel": "Cancel",
+  "aria.previous": "Previous",
+  "aria.next": "Next",
+  "aria.hint": "Show hint"
 }