fix: harden update pipeline and restore a clean production build

- update-Nitrov3.sh: build CMS into .next-staging and swap atomically so a
  failed build never takes the live site down; auto-merge new variables
  from .env.example; validate env for duplicates/broken lines; restart the
  emulator/CMS only when rebuilt or unhealthy; fix step renumbering
- next.config.ts: support NEXT_DIST_DIR for staged production builds
- fix all TS errors (unused imports, missing tryDownloadCandidates helper)
  so tsc and the production build pass clean
- add Dockerfile/.dockerignore and switch docker-compose to a CMS container
- include prevailing UI/refactor changes (SurfaceCard, ticketing, tsconfig)

src/lib/foundation/action.ts

@@ -40,7 +40,7 @@ function fail(
 	return { ok: false, error, fieldErrors };
 }
 
-export { fail as actionError, ok as actionOk };
+export { ok as actionOk };
 
 interface AdminOpts<TSchema extends z.ZodType | undefined> {
 	/** Single slug, or any-of list (e.g. admin.moderation.edit OR mod.actions). */