chore: add release automation and /release skill

- Auto-tag workflow: detects Cargo.toml version bump on main push,
  creates and pushes git tag to trigger the release workflow.
  Uses github.event.before for reliable diff, guards against null SHA
  on first push, and checks remote tags before creating.
- /release Claude Code skill: guided release preparation with semver
  determination, confirmation phase, and PR creation.
- CHANGELOG updated with new automation entries.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mikkeldamsgaard

.claude/commands/release.md

@@ -28,7 +28,7 @@ Once confirmed:
 
 1. Fetch origin and create a branch: `release/vX.Y.Z` from `origin/main`.
 2. Bump version in `Cargo.toml` (the `version = "..."` field under `[package]`).
-3. Run `cargo check` to update `Cargo.lock`.
+3. Run `cargo check` to ensure the project builds successfully after the version bump.
 4. Update `CHANGELOG.md`:
    - Move everything under `## [Unreleased]` into a new `## [X.Y.Z] - YYYY-MM-DD` section (use today's date).
    - Leave `## [Unreleased]` empty (with just the heading).

.github/workflows/auto-tag.yml

@@ -12,12 +12,16 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          fetch-depth: 2
+          fetch-depth: 0
       - name: Check for version bump
         id: version
         run: |
           CURRENT=$(grep '^version' Cargo.toml | head -1 | sed 's/.*"\(.*\)"/\1/')
-          PREVIOUS=$(git show HEAD~1:Cargo.toml | grep '^version' | head -1 | sed 's/.*"\(.*\)"/\1/')
+          if [ "${{ github.event.before }}" = "0000000000000000000000000000000000000000" ]; then
+            PREVIOUS="$CURRENT"
+          else
+            PREVIOUS=$(git show ${{ github.event.before }}:Cargo.toml | grep '^version' | head -1 | sed 's/.*"\(.*\)"/\1/')
+          fi
           echo "current=$CURRENT" >> "$GITHUB_OUTPUT"
           echo "previous=$PREVIOUS" >> "$GITHUB_OUTPUT"
           if [ "$CURRENT" != "$PREVIOUS" ]; then
@@ -30,11 +34,22 @@ jobs:
         run: |
           VERSION="${{ steps.version.outputs.current }}"
           TAG="v${VERSION}"
+          if git ls-remote --tags origin "refs/tags/$TAG" | grep -q .; then
+            echo "Tag $TAG already exists on origin, skipping"
+            exit 0
+          fi
           if git rev-parse "$TAG" >/dev/null 2>&1; then
-            echo "Tag $TAG already exists, skipping"
+            echo "Tag $TAG already exists locally, skipping"
             exit 0
           fi
           git tag "$TAG"
-          git push origin "$TAG"
+          if ! git push origin "$TAG"; then
+            if git ls-remote --tags origin "refs/tags/$TAG" | grep -q .; then
+              echo "Tag $TAG was created concurrently on origin, skipping"
+              exit 0
+            fi
+            echo "Failed to push tag $TAG"
+            exit 1
+          fi
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}