refactor: rename changelog/ to changelog.d/, use setuptools_scm CLI

- Rename `changelog/` to `changelog.d/` to match the convention
  expected by the `towncrier-fragments` version scheme in
  vcs-versioning. This makes `python -m setuptools_scm --strip-dev`
  correctly detect fragment types and compute the release version.

- Remove `scripts/compute_version.py` — the setuptools_scm CLI
  with `--strip-dev` replaces it entirely.

- Update `prepare-release.yml` and `scripts/release.py` to use the CLI.

- Add `setuptools-scm[toml]>=10.0` to the tox release env deps.

Co-authored-by: Cursor AI <ai@cursor.sh>
Co-authored-by: Anthropic Claude Opus 4 <claude@anthropic.com>

Author: 3 people

.github/workflows/prepare-release.yml

@@ -26,12 +26,13 @@ jobs:
           python-version: "3.13"
 
       - name: Install dependencies
-        run: pip install "setuptools-scm[toml]>=10.0" packaging towncrier
+        run: pip install "setuptools-scm[toml]>=10.0" towncrier
 
       - name: Compute next version
         id: version
         run: |
-          VERSION=$(python scripts/compute_version.py) || exit 0
+          VERSION=$(python -m setuptools_scm --strip-dev) || exit 0
+          if [ -z "$VERSION" ]; then exit 0; fi
           echo "version=$VERSION" >> "$GITHUB_OUTPUT"
           echo "branch=release-$VERSION" >> "$GITHUB_OUTPUT"
           echo "Computed version: $VERSION"

RELEASING.rst

@@ -8,7 +8,7 @@ version scheme (``feature`` → minor, ``bugfix`` → patch, ``removal`` → maj
 Automated flow
 ~~~~~~~~~~~~~~
 
-#. Contributors add changelog fragments (``changelog/<id>.<type>.rst``) in
+#. Contributors add changelog fragments (``changelog.d/<id>.<type>.rst``) in
    their pull requests as usual.
 
 #. Every push to ``main`` triggers the ``prepare-release`` workflow, which: