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/voice/realtimeConnection.js

@@ -61,7 +61,7 @@ export class RealtimeConnection {
     this.input.pushToTalkKeyHeld = pushToTalkKeyHeld;
     this.input.spaceKeyHeld = spaceKeyHeld;
     if (!window.RTCPeerConnection || !navigator.mediaDevices?.getUserMedia) {
-      this.setStatus('error', t('setup.voice.detail.microphoneUnavailable'));
+      this.setStatus('error', t('WebRTC microphone support unavailable'));
       return;
     }
 
@@ -80,7 +80,7 @@ export class RealtimeConnection {
     // — this is what "applies next session" means.
     this.cost.prepareSession();
     this.syncCostUi();
-    this.setStatus('connecting', t('setup.voice.detail.requestingMicrophone'));
+    this.setStatus('connecting', t('Requesting microphone'));
     this.debugLog('session.starting', {
       epoch,
       tier: this.cost.voiceTier,
@@ -181,9 +181,9 @@ export class RealtimeConnection {
         if (!ownsChannel()) return;
         const detail = this.input.pushToTalkMode
           ? this.input.pushToTalkKeyHeld
-            ? t('setup.voice.detail.releaseSpaceSend')
-            : t('setup.voice.detail.holdSpaceTalk')
-          : t('setup.voice.detail.askOrCommand');
+            ? t('Release Space to send')
+            : t('Hold Space to talk')
+          : t('Ask or command');
         this.setStatus('listening', detail);
         this.debugLog('data_channel.open', {
           connection: this.connectionDiagnostics(dataChannel),