Every build runs on 3.14

JP builds with 3.14 now, so the workflows do too. The lint job moves from 3.10, the
packaging build job and the release's site rebuild and PyPI build from 3.12, and the
installers from 3.10. The test matrix is untouched: it still runs every version from
3.10 up, because 3.10 is still the floor.

The installers' comment said the oldest Python was chosen on purpose, for reach. The
reach that matters on Linux comes from glibc, and that comes from the runner, so the
Linux legs stay on ubuntu-22.04 and the comment now says that. The binaries carry 3.14
from the next release; 0.9.0's were built on 3.10.

The changelog gains the 3.14 entry JP wrote in another session, plus a line for the
downloads.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/github-release.yml

@@ -243,7 +243,7 @@ jobs:
 
       - uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: "3.14"
 
       - name: Rebuild the site from this release
         run: |