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i18n: complete every module's `en` catalog, and gate it in CI #319

Job	Run time
JS typecheck	35s
Python lint & format	15s
Python typecheck	17s
Python tests	4m 0s
JS tests (Vitest)	30s
JS build (Vite)	46s
E2E smoke (Playwright)	3m 9s
Package build (release dry-run)	14s
JS lint & format	18s
Perf guards (Playwright)	1m 48s
File size (300-line cap)	17s
PR checks	4s
	12m 13s