Core: Include notebooks in outdated checks and split retranslation progress by type

[skytin1004]

Purpose

• Include Jupyter notebooks in outdated checks and orphan cleanup to keep translations accurate.
• Improve CLI UX by splitting retranslation progress into separate bars for notebooks and markdowns.
• Make markdown metadata parsing robust to unlabeled HTML comments, unblocking tests and legacy files.

Description

• Project-wide

  • Added notebook awareness across the translation lifecycle:
    • Outdated checks now consider .ipynb files.
    • Orphan cleanup deletes translated notebooks whose original has moved/been removed.
    • Directory synchronization treats .ipynb as relevant when creating/removing language directories.
  • Improved progress reporting by splitting retranslation into:
    • “📓 Retranslating outdated notebooks”
    • “📝 Retranslating outdated markdowns”

• Why necessary

  • Previously, notebooks were not consistently handled in outdated checks or orphan cleanup, causing stale translated notebooks to persist.
  • The single progress bar obscured which file types were being processed.
  • Tests used an unlabeled metadata format; the strict parser caused orphan cleanup to skip files.

Related Issue

Does this introduce a breaking change?

When developers merge from main and run the server, azd up, or azd deploy, will this produce an error?

• Yes
• No

Type of change

• Bugfix
• Feature
• Code style update (e.g., formatting, local variables)
• Refactoring (no functional or API changes)
• Documentation content changes
• Other... Please describe:

Checklist

Before submitting your pull request, please confirm the following:

• I have thoroughly tested my changes: I confirm that I have run the code and manually tested all affected areas.
• All existing tests pass: I have run all tests and confirmed that nothing is broken.
• I have added new tests (if applicable): Tests around notebook orphan cleanup and unlabeled metadata parsing are covered by existing suites.
• I have followed the Co-op Translator’s coding conventions.
• I have documented my changes (if applicable): Updated behavior is reflected in logs and code comments.

Additional context

• Logs now clearly indicate per-type retranslation progress and notebook orphan deletions.
• The metadata parser change is backward compatible and handles legacy content without affecting current labeled format.

[skytin1004]

I have reviewed the changes and everything looks good.