Automate releases from tags

Releases were manual and had drifted: v0.2.0 and v0.2.1 were tagged but never
released, so the releases page jumped v0.1.0 -> v0.3.0 and hid the fix for the
incident that took every app down.

Pushing a v* tag now runs the full suite and cuts a GitHub release whose body is
the matching CHANGELOG.md section -- one source of truth for release notes, so
there is no second place for them to be wrong.

The workflow refuses to publish when:
  - the tests, ruff, or bash -n fail (a tagged commit is what people install; it
    must be at least as good as main)
  - the tag does not match the VERSION= declared by every script
  - CHANGELOG.md has no section for the tag, or the section is empty

That version check is not theoretical: VERSION= had drifted to three different
values across install.sh / uninstall.sh / recover.sh / apply.sh and nothing
noticed until this release. tests/test_release_notes.py now asserts the scripts
agree with each other and with the newest CHANGELOG entry, so the drift cannot
come back.

workflow_dispatch takes an existing tag, so releases can be backfilled for tags
that were pushed before this existed.

106 tests, ruff and shellcheck clean.

.github/workflows/ci.yml

@@ -51,7 +51,7 @@ jobs:
         run: python -m pip install --upgrade pip pytest ruff
 
       - name: ruff
-        run: ruff check patch tests
+        run: ruff check patch tests tools
 
       - name: pytest
         run: pytest tests -v