chore: add release automation and /release skill

[mikkeldamsgaard]

Summary

• Auto-tag workflow (.github/workflows/auto-tag.yml): Runs on push to main when Cargo.toml changes. Compares the version with the previous commit — if it changed, creates and pushes a vX.Y.Z tag. This triggers the existing release workflow (Docker build, crates.io publish).
• /release skill (.claude/commands/release.md): A guided release preparation command for Claude Code. Determines the next semver version from changelog + commits, presents a confirmation to the user, then creates a release PR with version bump + changelog update.

New release flow

1. Run /release in Claude Code
2. Claude determines the version, shows a summary, asks for confirmation
3. Claude creates a release PR (version bump + changelog)
4. Merge the PR
5. Auto-tag workflow detects the version change, creates the tag
6. Release workflow builds Docker images and publishes to crates.io

Test plan

• Verify auto-tag workflow syntax is valid
• Verify /release skill appears in Claude Code (/?)
• After merge, confirm no tag is created (since Cargo.toml version is unchanged in this PR)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds repository automation and guidance to streamline releases by auto-tagging version bumps on main and documenting a /release command workflow for Claude Code.

Changes:

• Introduces a new GitHub Actions workflow to create vX.Y.Z tags when Cargo.toml version changes on main.
• Adds a Claude Code /release command guide to prepare a release PR (version bump + changelog update).
• Updates CHANGELOG.md to document the new release flow components.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
CHANGELOG.md	Documents the new auto-tag workflow and /release command under Unreleased.
.github/workflows/auto-tag.yml	Adds CI workflow that detects version bumps and pushes a vX.Y.Z tag.
.claude/commands/release.md	Adds guided release instructions for creating a release PR.

---

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[Copilot]

HEAD~1 only compares against the immediately previous commit. On pushes that include multiple commits (or merges), this can miss a version bump that happened earlier in the push (or compare against the wrong base). Use the push event's before SHA (e.g., ${{ github.event.before }}) or explicitly diff Cargo.toml between ${{ github.event.before }} and ${{ github.sha }} to reliably detect version changes for the whole push.

Suggested change

	fetch-depth: 2
	- 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/')
	fetch-depth: 0
	- name: Check for version bump
	id: version
	run: |
	CURRENT=$(grep '^version' Cargo.toml | head -1 | sed 's/.*"\(.*\)"/\1/')
	PREVIOUS=$(git show ${{ github.event.before }}:Cargo.toml | grep '^version' | head -1 | sed 's/.*"\(.*\)"/\1/')

[Copilot]

The tag existence check uses git rev-parse "$TAG", which only checks locally fetched tags. In a shallow checkout this may not include existing remote tags, causing git push to fail when the tag already exists on origin. Prefer checking the remote (git ls-remote --tags origin "refs/tags/$TAG") or fetching tags before the check, and handle a push rejection gracefully.

Suggested change

	if git rev-parse "$TAG" >/dev/null 2>&1; then
	echo "Tag $TAG already exists, skipping"
	exit 0
	fi
	git tag "$TAG"
	git push origin "$TAG"
	# Check if the tag already exists on the remote
	if git ls-remote --tags origin "refs/tags/$TAG" | grep -q .; then
	echo "Tag $TAG already exists on origin, skipping"
	exit 0
	fi
	# Also check if the tag exists locally
	if git rev-parse "$TAG" >/dev/null 2>&1; then
	echo "Tag $TAG already exists locally, skipping"
	exit 0
	fi
	git tag "$TAG"
	# Push the tag; if it fails, re-check the remote to handle concurrent creation
	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

[Copilot]

This step says cargo check will update Cargo.lock, but cargo check typically won't change the lockfile unless dependency resolution changes; bumping the package version alone won't do that. If the goal is just validation, reword to reflect that; if the goal is to ensure a lockfile exists/updates, use the appropriate Cargo command (e.g., generating/updating the lockfile) instead.

Suggested change

	3. Run `cargo check` to update `Cargo.lock`.
	3. Run `cargo check` to ensure the project builds successfully after the version bump.