chore: split i18n and bs-docs dirty checks in typecheck workflow (#14849)

## Summary

Split generated-file validation in the `typecheck` workflow so i18n
outputs and BS docs outputs are checked separately.

This fixes a misleading CI failure message: previously, CI could fail
due to i18n-generated changes like
`packages/frontend/i18n/src/i18n.gen.ts`, but only suggested running
`yarn typecheck && yarn affine bs-docs build`, which does not regenerate
those files.

## Changes

- validate i18n-generated changes immediately after `yarn affine
@affine/i18n build`
- keep ignoring `packages/frontend/i18n/src/i18n-completenesses.json` in
CI as before
- leave `yarn typecheck` as a separate step
- make the BS docs step only check for changes introduced by `yarn
affine bs-docs build`

## Result

CI now gives the correct remediation command depending on which
generated files are out of date:
- i18n issues: `yarn affine @affine/i18n build`
- docs/typecheck issues: `yarn typecheck && yarn affine bs-docs build`

## Testing

- verified the updated workflow YAML parses successfully


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Enhanced build validation for internationalization code generation to
ensure generated changes are properly committed before proceeding. The
validation now occurs immediately after code generation runs, providing
faster feedback during the build process.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->