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/locationNavigation.js

@@ -89,9 +89,8 @@ export class LocationNavigation {
       this._collapsePOIRow();
       this._updateLocationMiniStatus();
     } else if (change.type === 'missing')
-      this._showToast(t('cockpit.location.toastNotFound'));
-    else if (change.type === 'failed')
-      this._showToast(t('cockpit.location.toastSearchFailed'));
+      this._showToast(t('Location not found'));
+    else if (change.type === 'failed') this._showToast(t('Search failed'));
     else if (change.type === 'settled')
       this._settleLocationSearchUi(change.generation);
     else if (
@@ -280,7 +279,7 @@ export class LocationNavigation {
 
   _toggleOrbit() {
     if (!this._currentTarget) {
-      this._showToast(t('cockpit.location.toastFlyToPoiFirst'));
+      this._showToast(t('Fly to a POI first'));
       return;
     }
 
@@ -382,11 +381,11 @@ export class LocationNavigation {
       };
       this._resetGlobeBtn?.setAttribute(
         'aria-label',
-        t('cockpit.hud.resetGlobeAria'),
+        t('Reset to full globe view'),
       );
       this._cockpitResetGlobeBtn?.setAttribute(
         'aria-label',
-        t('cockpit.hud.resetGlobeCockpitAria'),
+        t('Reset cockpit to full globe view'),
       );
       this._globeResetPromise = null;
       this._cancelGlobeReset = null;
@@ -402,11 +401,11 @@ export class LocationNavigation {
     }, 4200);
     this._resetGlobeBtn?.setAttribute(
       'aria-label',
-      t('cockpit.hud.resettingGlobeAria'),
+      t('Resetting to full globe view'),
     );
     this._cockpitResetGlobeBtn?.setAttribute(
       'aria-label',
-      t('cockpit.hud.resettingGlobeCockpitAria'),
+      t('Resetting cockpit to full globe view'),
     );
     const target = flyToGlobeView(this.viewer, {
       onComplete: () => finish(false),