refactor(i18n): key messages by English text; add Russian

Replace the semantic keys with the English source text, so code reads as the
UI does and English needs no catalog: t('Save keys'), tn(count, one, other)
for plurals, msg() for text stored in data, and bare data-i18n* markup that
translates the element's own English. Other languages are one flat JSON each.

- Simplify src/i18n: drop namespaces, the configurable locale pair
  (GEV_DEFAULT_LOCALE / GEV_SECONDARY_LOCALE) and its build defines. Locale
  comes from ?lang=, the stored choice, then browser languages.
- Add scripts/i18n.mjs (npm run i18n): extracts every message from t/tn/msg
  and markup, and fails on missing, unused, placeholder-mismatched or
  wrongly-shaped plural entries. npm test runs it via catalog.test.mjs.
- Add Russian (src/i18n/locales/ru.json, 833 messages), started from the
  community catalog in #312 and reviewed against the current English.
- Fix data-i18n placed on parents that would wipe their children (cockpit
  LEVEL and local weather cells, first-run EXPLORE MANUALLY tile), and a
  doubled degree sign in the TRACK ACQUIRED signal.
- Rewrite docs/TRANSLATORS.md for the new workflow; drop sections the earlier
  merge resurrected in docs/CURRENT-STATE.md.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/ui/shellFeedback.js

@@ -9,7 +9,7 @@ import {
   reduceTrafficSyncFeedback,
 } from '../loadingFeedback.js';
 import { setSplitFlapText, disposeSplitFlap } from '../splitFlap.js';
-import { t } from '../i18n/index.js';
+import { t, msg } from '../i18n/index.js';
 
 // loadingFeedback.js composes the shared status copy inside the portable
 // node/browser graph (the server-side HUD summary reads the same modules), so
@@ -17,17 +17,17 @@ import { t } from '../i18n/index.js';
 // the closed label vocabulary to the catalog, and pass anything unrecognized
 // (a live provider error) through verbatim (docs/TRANSLATORS.md).
 const STATUS_LABEL_KEYS = Object.freeze({
-  'LOADING LIVE DATA': 'shell.status.loadingLiveData',
-  'LOAD COMPLETE': 'shell.status.loadComplete',
-  'LOAD CANCELLED': 'shell.status.loadCancelled',
-  'LOAD FAILED': 'shell.status.loadFailed',
-  'LIVE DATA OFF': 'shell.status.liveDataOff',
-  'MAPPED SITES LOADED': 'shell.status.mappedSitesLoaded',
-  'RETRYING MAPPED SITES': 'shell.status.retryingMappedSites',
-  'FETCHING MAPPED SITES': 'shell.status.fetchingMappedSites',
-  'TURNING OFF LIVE DATA': 'shell.status.turningOffLiveData',
-  'REFRESHING LIVE DATA': 'shell.status.refreshingLiveData',
-  'syncing road network': 'shell.status.trafficSyncing',
+  'LOADING LIVE DATA': msg('LOADING LIVE DATA'),
+  'LOAD COMPLETE': msg('LOAD COMPLETE'),
+  'LOAD CANCELLED': msg('LOAD CANCELLED'),
+  'LOAD FAILED': msg('LOAD FAILED'),
+  'LIVE DATA OFF': msg('LIVE DATA OFF'),
+  'MAPPED SITES LOADED': msg('MAPPED SITES LOADED'),
+  'RETRYING MAPPED SITES': msg('RETRYING MAPPED SITES'),
+  'FETCHING MAPPED SITES': msg('FETCHING MAPPED SITES'),
+  'TURNING OFF LIVE DATA': msg('TURNING OFF LIVE DATA'),
+  'REFRESHING LIVE DATA': msg('REFRESHING LIVE DATA'),
+  'syncing road network': msg('syncing road network'),
 });
 
 function localizeStatusLabel(label) {
@@ -41,8 +41,8 @@ const RETRY_DETAIL_RE = /^(?:ALPR cameras · )?retrying in (\d+)s$/;
 function localizeStatusDetail(detail) {
   if (typeof detail !== 'string' || !detail) return detail;
   const match = detail.match(RETRY_DETAIL_RE);
-  if (match) return t('shell.status.retryingIn', { seconds: match[1] });
-  if (detail.trim() === 'retry pending') return t('shell.status.retryPending');
+  if (match) return t('retrying in {seconds}s', { seconds: match[1] });
+  if (detail.trim() === 'retry pending') return t('retry pending');
   return detail;
 }