feat: surface previous translation memory hints in editor ( Issue #502 )

[zanzo2003]

Summary ( PR for Issue #502 )

• preload prior StringTranslations per segment so the React editor can reference them when the source text changes
• expose historic translation/comment/author to the UI and render a “Previous translation” banner with a reuse shortcut
• add a regression test that covers the stale-segment scenario for pages

Testing

• python3 -m pytest wagtail_localize/tests/
  test_edit_translation.py::TestGetEditTranslationView::test_segments_include_previous_translation_when_source_changes
  --ds=wagtail_localize.test.settings
• npm run build (after npm install)
• Manual: change EN source text, open FR translation editor, verify banner + “Reuse previous translation” button saves
  cleanly

Adding test and Browser screen shots

[zanzo2003]

Previous source and tests screenshots

[shreyasbhaskar2001]

Some minor feedbacks!!

• wagtail_localize/locales/templates/wagtaillocales/edit.html:29, wagtail_localize/templates/wagtail_localize/admin/
  _components.html:7, wagtail_localize/templates/wagtail_localize/admin/submit_translation.html:24, wagtail_localize/
  templates/wagtail_localize/admin/update_translations.html:36: the includes for wagtailadmin/shared/
  non_field_errors.html have dropped out, so form-level validation errors (including component-level ones) will no
  longer be rendered. This regresses fixes merged recently—please restore the includes (a rebase onto current main
  should bring them back).
• wagtail_localize/locales/views.py:75 and wagtail_localize/locales/templates/wagtaillocales/index.html:3: removing
  paginate_by = 20 and the pagination block undoes the new locale list pagination. On sites with many locales this will
  make the index slow and unwieldy, and the corresponding tests were also deleted. Reinstating the pagination logic
  (again, via rebase) is important to avoid that regression.

Highlights

• Nice work enriching TranslationEditor with a previousTranslation payload and UI so translators can re-use the last
  human translation when the source string changes. This was a major pain point for the user, saw a discussion dating back to Jan 22

• The backend changes in edit_translation.py efficiently gather the historical translation metadata and you added
  test_segments_include_previous_translation_when_source_changes, which gives good coverage of the new behaviour.

  Additionally @thibaudcolas , can you also check if these feedbacks are valid from you p.o.v ? I think this adds some good value to the product .

[Phinart98]

Looks like the closing } for &--green got removed here along with the blank lines. Without it, &--red ends up nested inside &--green, so it'd compile to .icon--green--red instead of .icon--red — which would break the red error icon styling.

[zanzo2003]

Hey @Phinart98 , thanks for pointing that out !! totally missed that brace. I have updated the PR. Please let me know if there is anything else ? Thanks!