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/data/militaryAwarenessEngine.js

@@ -84,14 +84,14 @@ export function summarizeAwarenessCohort(
       relationship: AWARENESS_RELATIONSHIP.UNKNOWN,
       count: null,
       nearest: [],
-      reason: t('layers.awareness.reason.feedUnavailable'),
+      reason: t('feed unavailable'),
     };
   if (stale)
     return {
       relationship: AWARENESS_RELATIONSHIP.UNKNOWN,
       count: null,
       nearest: [],
-      reason: t('layers.awareness.reason.feedStale'),
+      reason: t('feed stale'),
     };
   const normalized = (Array.isArray(items) ? items : [])
     .filter(
@@ -108,8 +108,8 @@ export function summarizeAwarenessCohort(
     count: normalized.length,
     nearest: normalized.slice(0, limit),
     reason: normalized.length
-      ? t('layers.awareness.reason.nearby')
-      : t('layers.awareness.reason.none'),
+      ? t('observed or mapped nearby context')
+      : t('no observed or mapped objects in current feeds'),
   };
 }