(feat): check audio when selected

[kyeunga25]

Summary

• start bounded local audio structure inspection immediately after a metadata-valid selection
• keep generation and upload actions disabled until the current file passes, with bilingual accessible status
• abort stale checks after replacement or navigation, and repeat inspection before upload creation
• cover valid, renamed-invalid, replacement-race, and mobile-width flows with synthetic fixtures

Verification

• pnpm typecheck
• pnpm lint
• pnpm format
• pnpm test:unit (479 passed)
• pnpm test:api (138 passed)
• pnpm test:local-ai
• pnpm test:e2e (51 passed)
• pnpm build
• pnpm public-config:check
• pnpm audit --audit-level=high
• pnpm audit --prod --audit-level=high
• git diff --check

Release boundary

No migration, dependency, public configuration, provider, payment, secret, or production capability flag changes. Real generation and paid features remain disabled.