New script `scripts/i18n/sync-ui-keys.mjs` replicates keys present in
`src/i18n/messages/en.json` into every other locale catalog, marking
missing strings with a `__MISSING__:<english_value>` sentinel so the
drift is auditable and recoverable.
The script also accepts `--translate-markers` to call the OmniRoute
translation backend (same env vars as run-translation.mjs) and replace
those placeholders with real translations. Bounded concurrency, fail-
fast on missing env vars, and a `--dry-run` mode mirror the existing
docs translation pipeline.
Adds the matching `i18n:sync-ui` / `i18n:sync-ui:dry` npm scripts and
`i18n:check-ui-coverage` (next commit) wiring placeholder so the JSON
files can be backfilled with `npm run i18n:sync-ui`.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
