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/cockpitPresentation.js

@@ -1,5 +1,5 @@
 /** Pure formatting and fixed presentation constants used by Cockpit components. */
-import { t } from '../i18n/index.js';
+import { t, msg } from '../i18n/index.js';
 
 export const COCKPIT_HEADING_SLEW_DPS = 28;
 
@@ -46,21 +46,21 @@ export const COCKPIT_REGIONAL_REFRESH_DISTANCE_M = 25_000;
 export const COCKPIT_BRIEF_PAGES = [
   {
     id: 'signals',
-    kickerKey: 'cockpit.brief.kicker',
-    subtitleKey: 'cockpit.brief.subtitle',
-    sourceKey: 'cockpit.brief.sourceNote',
+    kickerKey: msg('LIVE SIGNALS'),
+    subtitleKey: msg('OBSERVED / MAPPED PINGS'),
+    sourceKey: msg('SOURCE-BACKED EVENTS · NO SYNTHETIC NEWS'),
   },
   {
     id: 'news',
-    kickerKey: 'cockpit.brief.kickerNews',
-    subtitleKey: 'cockpit.brief.subtitleNews',
+    kickerKey: msg('REGIONAL NEWS'),
+    subtitleKey: msg('LATEST LOCATION-MATCHED REPORTING'),
     // RSS provider attribution is a keep-English boundary string.
     source: 'GOOGLE NEWS RSS · LOCATION QUERY · RECENT',
   },
   {
     id: 'local',
-    kickerKey: 'cockpit.brief.kickerLocal',
-    subtitleKey: 'cockpit.brief.subtitleLocal',
+    kickerKey: msg('LOCAL INFO'),
+    subtitleKey: msg('PLACE / CONDITIONS / POSITION'),
     // Data-source attribution is a keep-English boundary string.
     source: 'NATURAL EARTH · OPEN-METEO · UTC',
   },
@@ -84,17 +84,17 @@ export function isRenderedOnScreen(element) {
 
 export function formatCockpitBriefAge(value) {
   const timestamp = Date.parse(value);
-  if (!Number.isFinite(timestamp)) return t('cockpit.brief.age.timeUnknown');
+  if (!Number.isFinite(timestamp)) return t('TIME UNKNOWN');
   const minutes = Math.max(0, Math.round((Date.now() - timestamp) / 60_000));
-  if (minutes < 60) return t('cockpit.brief.age.minutes', { count: minutes });
+  if (minutes < 60) return t('{count}M AGO', { count: minutes });
   const hours = Math.round(minutes / 60);
   return hours < 48
-    ? t('cockpit.brief.age.hours', { count: hours })
-    : t('cockpit.brief.age.days', { count: Math.round(hours / 24) });
+    ? t('{count}H AGO', { count: hours })
+    : t('{count}D AGO', { count: Math.round(hours / 24) });
 }
 
 export function formatCockpitWindDirection(value) {
-  if (!Number.isFinite(value)) return t('cockpit.brief.wind.dirUnknown');
+  if (!Number.isFinite(value)) return t('DIR UNKNOWN');
   const labels = ['N', 'NE', 'E', 'SE', 'S', 'SW', 'W', 'NW'];
   const normalized = ((value % 360) + 360) % 360;
   return `${labels[Math.round(normalized / 45) % labels.length]} · ${Math.round(normalized)}°`;