Fix system contract drift and default mode language

[RajjjAryan]

Summary

Closes #74.
Closes #75.
Closes #76.
Closes #77.
Closes #78.

• expand updater coverage so tracked system files are either updateable or explicitly user/generated exclusions
• refresh DATA_CONTRACT.md for current user/system boundaries
• add Spanish and Japanese CV section labels and locale tests
• translate root scan.md and pdf.md back to English baseline instructions
• add top-level Python virtualenv ignores
• update README localized-mode list for shipped es and ja packs

Verification

• node --test tests/repo-contract.test.mjs tests/feature-entrypoints.test.mjs tests/cv-i18n.test.mjs
• npm test (107 passed, 0 failed, 3 expected no-user-data warnings)
• git diff --check