Prepare the 0.3.0 release, and keep tags off pre-squash commits

[keithlostracco]

The v0.3.0 tag was pushed to 85de526, the pre-squash tip of the branch behind #54. Squash-merging rewrote that commit as 6026ca2, so the tag points at a commit reachable only from the tag. The release workflow didn't publish it, correctly: CHANGELOG.md had no ## [0.3.0] section, since those entries were still under [Unreleased]. No release was created, so there is nothing published to retract.

This prepares the release properly and stops the same mistake from recurring.

Release prep

• [Unreleased] closed as ## [0.3.0] - 2026-07-26, with the compare links.
• project(anim VERSION ...) bumped to 0.3.0. It had been left at 0.2.0, and it is the single source of the version for the installed find_package config, so tagging without this would have shipped a package claiming 0.2.0.

Workflow fixes

• The release job now checks that the tagged commit is an ancestor of main before publishing, and fails with a message saying to re-tag the merged commit. This needs fetch-depth: 0, which that checkout did not set.
• The release-notes extraction interpolated the version into an awk regex, where [0.3.0] is a character class rather than a literal. Whether the escaping survived depended on the awk in use: mawk keeps the backslash so it worked on ubuntu-latest, but gawk drops it and matches nothing. Had the runner image ever switched, every release would have failed the non-empty guard with no obvious cause. The heading is now matched by prefix with index(), so no awk flavour can turn a release into an empty description.
• Issue links are inlined rather than reference-style. A section ends at the first link reference block, so ([#52]) resolved in the changelog but rendered as literal text in the release description generated from it.

Verification

Extraction dry-run under gawk 5.0.0 against the updated changelog:

Version	Bytes	Result
0.3.0	2974	full section
0.2.0	2826	full section, matches the published v0.2.0 body
0.1.2	194	stops before the next heading
0.1.0	218	stops before the trailing comment and link block
9.9.9	0	empty, so the existing guard still fails the release

72/72 tests pass locally; the generated anim-config-version.cmake reports 0.3.0.

After merge

The misplaced v0.3.0 tag is deleted and re-created on the merge commit, then pushed to publish the release. Anything pinned to 85de526 needs repointing.