Add release make target and /release skill

[andreashasse]

Summary

• Adds make release target that validates branch/sync state, prompts for tag, publishes to hex.pm, and creates a GitHub release
• Adds .claude/skills/release/SKILL.md — a /release skill that analyzes commits, suggests a semver bump, updates CHANGELOG.md and README.md, and creates a release branch/PR

Test plan

• Verify make release runs correctly from main with a clean working tree
• Verify /release skill guides through version bump and file updates correctly

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a release workflow for this repository by introducing a make release target and a Claude “/release” skill to guide versioning/changelog updates and release steps.

Changes:

• Add make release target with branch/sync/clean-tree validation, Hex publish, and GitHub release creation.
• Add .claude/skills/release/SKILL.md documenting a guided release process (semver suggestion, changelog/README updates, release branch/PR flow).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 9 comments.

File	Description
Makefile	Adds a new release target to tag, publish to Hex, and create a GitHub release.
.claude/skills/release/SKILL.md	Adds a /release skill document describing a release preparation workflow.

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[Copilot]

This skill instructs the user to read/update CHANGELOG.md, but the repo currently doesn't include that file. Either add a CHANGELOG.md to the repository (and define its expected format) or adjust the skill to use whatever release notes source this repo actually maintains.

[Copilot]

The README guidance here doesn't match the current README.md in this repo: there is no Hex dependency example like {elli_openapi, "~> X.Y.Z"} (README currently shows a git dependency). Update the skill to match the actual installation instructions you want users to maintain.

Suggested change

	- Find and update the installation example: `{elli_openapi, "~> X.Y.Z"}`
	- Find and update the installation example that uses a git dependency, for example:
	```elixir
	{:elli_openapi, github: "elli-lib/elli_openapi", tag: "vX.Y.Z"}

[Copilot]

The git command in Step 2 is overly complex and uses --since=<date of last tag commit>, which can include unrelated commits (e.g., if commits were authored before that date but merged after). A more reliable way to list changes since the last tag is a range like <last_tag>..HEAD (with a fallback when no tags exist).

Suggested change

	git log --oneline --since="$(git log -1 --format=%ai $(git describe --tags --abbrev=0 2>/dev/null || echo HEAD))" 2>/dev/null || git log --oneline -20
	git describe --tags --abbrev=0 >/dev/null 2>&1 && git log --oneline "$(git describe --tags --abbrev=0)"..HEAD || git log --oneline -20

[Copilot]

The sed pattern that extracts the changelog section uses the raw tag in a regex (/## \[$$tag\]/), so tags containing regex metacharacters (notably . in semantic versions) can match unintended headings. Also, when the matching section is the last entry in the file (no following ## [), sed '$d' will drop the final line of the notes. Consider a parser that treats the tag literally and handles EOF correctly (e.g., awk with exact string match, or perl -pe), or rely on gh release create --notes-file/--generate-notes.

Suggested change

	gh release create "$$tag" --title "v$$tag" --notes "$$(sed -n "/## \[$$tag\]/,/## \[/p" CHANGELOG.md | sed '$$d' | tail -n +2)" && \
	gh release create "$$tag" --title "v$$tag" --notes "$$(awk -v tag="$$tag" ' \
	$$0 == "## [" tag "]" {found=1; next} \
	found && /^## \[/ {exit} \
	found {print} \
	' CHANGELOG.md)" && \

[Copilot]

The tag prompt suggests entering something like v1.0.0, but the release title is set to v$$tag, which will produce titles like vv1.0.0. Decide whether tags include the leading v and keep it consistent across the prompt, the tag name, and the GitHub release title.

Suggested change

	gh release create "$$tag" --title "v$$tag" --notes "$$(sed -n "/## \[$$tag\]/,/## \[/p" CHANGELOG.md | sed '$$d' | tail -n +2)" && \
	gh release create "$$tag" --title "$$tag" --notes "$$(sed -n "/## \[$$tag\]/,/## \[/p" CHANGELOG.md | sed '$$d' | tail -n +2)" && \