Fix scheduled status i18n build regression

[LeonSGP43]

Summary

• add the missing scheduled key to the board i18n type definition
• add English fallback scheduled entries to the remaining locale files so every translation matches the shared schema
• restore the Web UI build path that was broken by the scheduled status addition

Closes #28502

Testing

• git diff --check
• env -u HTTP_PROXY -u HTTPS_PROXY -u ALL_PROXY -u http_proxy -u https_proxy -u all_proxy /opt/homebrew/bin/node /opt/homebrew/lib/node_modules/npm/bin/npm-cli.js ci
• env -u HTTP_PROXY -u HTTPS_PROXY -u ALL_PROXY -u http_proxy -u https_proxy -u all_proxy /opt/homebrew/bin/node /opt/homebrew/lib/node_modules/npm/bin/npm-cli.js run build

[alt-glitch]

Partially overlaps with already-merged #28549 (which fixed types.ts). The locale file additions here are still needed, but competing PR #28534 covers the same scope. Closes #28502.

[teknium1]

Automated hermes-sweeper review: this PR appears to be fully implemented on current main now.

Evidence:

• web/src/i18n/types.ts:778 and web/src/i18n/types.ts:788 now declare scheduled: string in both board i18n type blocks.
• The affected locale files now include matching scheduled entries; for example, web/src/i18n/es.ts:712 and web/src/i18n/es.ts:722 cover the label and help text.
• The type-definition part landed in 1335ce996d000def7a93e33853606de693c06f7d (fix(web): add scheduled column to i18n type definitions (#28549)).
• The complete locale update landed in 709e37e19e954774caa3af40a93764bd8b893d35 (fix(dashboard): add scheduled kanban i18n strings (#28534)), matching the maintainer note in this PR's discussion that fix(dashboard): add scheduled Kanban i18n strings #28534 covered the remaining scope.
• The complete fix is contained in v2026.5.28 and later tags.

Thanks for the contribution; the same bug path has been resolved on main.