fix: restore MEARROW audition detail routes on Workers

[moony01]

Summary

• Unify audition detail loading with the Workers dynamic ASSETS pattern used by news.
• Generate active audition detail JSON under public/api/auditions-content/{locale}/{slug}.json and use a build-target-specific loader.
• Remove the Workers static route restriction and add a full ko/en audition detail browser smoke (10 details plus unknown-slug 404).

Verification

• pnpm test --run — 38 files, 159 tests passed
• pnpm lint — 0 errors (27 pre-existing warnings)
• pnpm build — passed
• pnpm workers:build — passed
• pnpm test:browser:workers-auditions — 10/10 detail pages HTTP 200, unknown slug HTTP 404, console/page errors 0

News publication status is unchanged; news remains staged for supplementation before republishing.