Railbase core v0.5.24

Unify the three drifting i18n stores (server embed, admin SPA, site SPA) into ONE Vault-backed _i18n catalog, served via /api/i18n with a ?scope= filter (server | admin | site) and edited live from the admin Translations tab.

• Single source of truth: a _i18n Vault system collection (row per locale+scope, JSON-string column).
• Scope-filtered bundle endpoint + version marker; the no-scope path stays SDK-compatible.
• Admin Translations editor repointed disk → Vault: full key universe per scope, live refresh on PUT, bulk import endpoint.
• Admin SPA fetches its scope from the catalog at runtime with the SHIPPED bundles as an offline floor (catalog overrides per-key) + a 60s version poll for live edits.
• Embedded en/ru remain the server-side floor.

i18n-only release on the v0.5.23 base (server + admin scopes). 10 admin UI languages ship bundled and are now operator-editable.