feat(ci): Fail frontend checks when vendored JS changes without its README

[geographybuff]

Fixes

Fixes: #8062

Summary

This PR adds the check the issue describes, then renames flatpickr's files and records it in the README. The commits follow the order the issue suggests, so CI shows the check working:

1. The check (f1c2b00).
   • check_vendored_js_readme in .github/scripts/frontend_checks.py fails the job (FAIL) when upstream files in js/third_party/ or js/alpine/ change but that directory's README.md doesn't.
   • Changes under js/alpine/components/ and js/alpine/composables/ are ignored. Each directory needs its own README change.
   • main() now also records the old side of an R line in --name-status, so moving a file into or out of a vendored directory counts. It also runs this check when no template or CSS file changed; until now it returned early in that case. Copies (C) leave their source untouched, so only their new path counts.
   • frontend-lint.yml now also triggers on js/third_party/** and js/alpine/**.
   • Tests: 11 new tests in test_frontend_checks.py, three of them through main() with real --name-status input. pytest .github/scripts passes 27 tests. Ruff (v0.14.11) check and format are clean. Pyrefly reports the same two existing errors in these files before and after.
2. The flatpickr rename (pushed next). flatpickr@4.6.13(.min).js and plugins/confirmDate@4.6.13(.min).js drop the version from their names, and the three require_script call sites are updated (corpus_search/date_selector ×2, docket_filter ×1). This commit should make the frontend checks fail.
3. The README section (pushed after that). A flatpickr section in js/third_party/README.md, following the htmx one, makes the check pass again.

On the README's sources: I compared the vendored files with jsDelivr's flatpickr@4.6.13 copies.

• flatpickr.min.js is byte-identical.
• The two unminified files match the CDN copies after running Prettier 2 with cl/.prettierrc.js (apart from whitespace on two blank lines), so they were reformatted, not modified. The README says so.
• confirmDate.min.js differs only in jsDelivr's "Minified by jsDelivr using Terser v5.x" comment.

The flatpickr stylesheet in css/third_party/ is out of scope, so it isn't touched.

Documentation

Once merged, the following documentation needs to be updated:

• None. The README change is part of this PR.

Deployment

This PR should:

• skip-deploy (skips everything below)
  • skip-web-deploy
  • skip-celery-deploy
  • skip-cronjob-deploy
  • skip-daemon-deploy

The renamed static files and the two templates are served by the web tier, so only web needs to deploy.

AI Disclosure

• No AI tools were used to create the content of this PR.
• Parts of this PR were created with the help of an AI tool, and I have carefully reviewed all of its content and take full responsibility for it.

AI model used: Claude Opus 5.5 (via Claude Code). It wrote the check, the tests and the README section, and ran the tests.

🤖 Generated with Claude Code

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[geographybuff]

Pushed the second commit (c0e6f6b): the flatpickr rename and the three call-site updates, with no README change. The Frontend Checks job should now fail on check_vendored_js_readme. The README section follows in the next commit.

[geographybuff]

The second commit failed Frontend Checks as expected (run 37778321331): check_vendored_js_readme reported that js/third_party/ changed without its README. Pushed the third commit (b22fb8b), which adds the flatpickr section to js/third_party/README.md, so the check should pass now.