feat(ci): add cliff.toml for structured changelog generation (#793)

Adds git-cliff configuration to generate structured changelogs from
Conventional Commits. Required by reusable-release.yml which calls
generate-release-notes wrapping git-cliff.

Note: omits the "chore: promote testing" skip rule — dakota uses OCI
digest promotions via "Publish Bluefin dakota", not squash promotion
commits.

Closes projectbluefin/common#609

Assisted-by: Claude Sonnet 4.5 via pi

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: castrojo

cliff.toml

@@ -0,0 +1,53 @@
+# git-cliff configuration for projectbluefin/dakota
+#
+# Generates structured changelogs from Conventional Commits.
+# Consumed by the release workflow (reusable-release.yml).
+#
+# Usage in release.yml:
+#   - name: Install git-cliff
+#     uses: taiki-e/install-action@<sha>
+#     with:
+#       tool: git-cliff
+#   - name: Generate changelog
+#     run: git cliff --latest --strip header > CHANGELOG.md
+
+[changelog]
+header = ""
+body = """
+{% for group, commits in commits | group_by(attribute="group") %}
+### {{ group | upper_first }}
+{% for commit in commits %}
+- {{ commit.message | split(pat="\n") | first | trim }}\
+  {% if commit.scope %} (**{{ commit.scope }}**){% endif %}\
+  ({{ commit.id | truncate(length=7, end="") }})\
+{% endfor %}
+{% endfor %}
+"""
+footer = """
+---
+*Generated by [git-cliff](https://git-cliff.org)*
+"""
+trim = true
+
+[git]
+conventional_commits = true
+filter_unconventional = true
+split_commits = false
+commit_parsers = [
+  { message = "^feat", group = "Features" },
+  { message = "^fix", group = "Bug Fixes" },
+  { message = "^perf", group = "Performance" },
+  { message = "^refactor", group = "Refactoring" },
+  { message = "^docs", group = "Documentation" },
+  { message = "^ci", group = "CI/CD" },
+  { message = "^chore\\(deps\\)", group = "Dependencies" },
+  { message = "^chore", group = "Miscellaneous" },
+  { message = "^build", group = "Build" },
+  { message = "^test", group = "Testing" },
+  { message = "^revert", group = "Reverts" },
+  # Skip merge commits
+  { message = "^Merge", skip = true },
+]
+filter_commits = false
+tag_pattern = "v[0-9].*"
+sort_commits = "newest"