feat: soft delete dataset draft

[kairoaraujo]

Summary

Draft deletion is currently a hard delete: the depositor's "delete" removes every triple of the draft, and it cannot be undone. This change makes draft deletion a soft delete, so the draft is flagged and hidden instead of removed, listed in a new "Deleted" section on /my/datasets, from where the depositor can restore it or permanently delete it behind a typed-title confirmation. The existing hard-delete query is reused unchanged for the permanent path. Uploaded files on S3 are not touched by either path.

Changes

• src/djehuty/schema/migrations/0002_add_dataset_is_deleted.ttl: new migration declaring the djht:is_deleted and djht:deleted_date predicates. Absence means "not deleted", so existing drafts need no back-fill.
• src/djehuty/web/resources/sparql_templates/soft_delete_dataset_draft.sparql: new — sets the deleted flag and timestamp, keeps all triples and the container→draft link. Same owner/supervisor authorization filter as the hard delete.
• src/djehuty/web/resources/sparql_templates/restore_dataset_draft.sparql: new — clears the deleted flag.
• src/djehuty/web/resources/sparql_templates/datasets.sparql: select/bind is_deleted + deleted_date; add an is_deleted filter (True/False/None → only-deleted / exclude-deleted / no-filter).
• src/djehuty/web/database.py: datasets() gains an is_deleted param (defaults to False, so every existing caller excludes soft-deleted drafts). New soft_delete_dataset_draft / restore_dataset_draft methods plus a shared cache-invalidation helper. The hard delete_dataset_draft is unchanged.
• src/djehuty/web/wsgi.py: new /restore and /delete-permanently routes and handlers; the two everyday delete callers now soft-delete; ui_my_data renders a "Deleted" bucket; the new-version-draft guard queries with is_deleted=None so a soft-deleted draft still blocks a second draft on the container.
• src/djehuty/web/resources/html_templates/depositor/my-data.html: "Deleted" section with Restore / Delete-permanently actions.
• src/djehuty/web/resources/html_templates/depositor/delete-dataset-permanently.html: new — typed-title confirmation page for permanent deletion.
• tests/e2e/tests/test_soft_delete.py: new — soft-delete moves a draft to Deleted, restore returns it to Drafts, permanent delete is title-gated, and restore access-control.
• tests/e2e/tests/test_versioning.py: regression test — a soft-deleted draft blocks creating a second new-version draft.
• tests/unit/test_migrate.py: isolate runner_real to a copy containing only 0001_initial.ttl, so the initial-seed assertions stay stable as real migrations accumulate.
• docs/knowledge-graph.md: new Soft-deleted drafts subsection under Datasets.
• doc/knowledge-graph.tex: new Soft-deleted drafts subsection under Datasets.

Approval Checklist

• I agree to follow Djehuty's code of conduct.
• I have read and I have follow the code contribution workflow.
• Code style and conventions were respected.
• Documentation has been updated where needed (README, docs, or examples).
• Review approved by at least one maintainer.
• Merge readiness (PR is squashed into a single commit and follows the commit template).

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[codecov]

Codecov Report

❌ Patch coverage is 7.69231% with 60 lines in your changes missing coverage. Please review.
✅ Project coverage is 17.22%. Comparing base (9ef6c31) to head (2e80b43).

Files with missing lines	Patch %	Lines
src/djehuty/web/wsgi.py	4.54%	42 Missing ⚠️
src/djehuty/web/database.py	14.28%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #226      +/-   ##
==========================================
- Coverage   17.28%   17.22%   -0.06%     
==========================================
  Files          21       21              
  Lines       10414    10477      +63     
  Branches     2022     2035      +13     
==========================================
+ Hits         1800     1805       +5     
- Misses       8425     8483      +58     
  Partials      189      189              

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[kairoaraujo]

Follow up on this PR:

• Remove the DELETE button from inside the form