fix: bump GitHub Actions to Node 24-compatible versions (#16)

[mmcky]

Summary

Resolves #16. GitHub forced Node 24 as the default runner runtime on 2026-06-02 (three days before this PR); Node 20 is fully removed on 2026-09-16. The action and its workflows still pinned Node-20 JS actions (actions/checkout@v4, astral-sh/setup-uv@v3, …), which now emit deprecation warnings and are on borrowed time.

What changed

Each action is bumped to its latest floating major tag that runs on Node 24, verified against the action's own runs.using field:

Action	Before	After	Runtime
actions/checkout	@v4	@v5	node24
astral-sh/setup-uv	@v3	@v7	node24
actions/setup-node (docs)	@v4	@v6	node24
actions/upload-pages-artifact (docs)	@v3	@v5	composite
actions/deploy-pages (docs)	@v4	@v5	node24

Files touched: action.yml, .github/workflows/ci.yml, .github/workflows/docs.yml.

Notes:

• astral-sh/setup-uv publishes no floating v8 major tag (only v8.0.0/.1/.2); v7 is the latest floating major and already runs on Node 24, so it's the right pin to stay on the floating-major convention.
• checkout pinned to @v5 (first/stable Node 24 major) rather than the brand-new @v6 — minimal, well-tested bump that fully satisfies the Node 24 requirement.
• Also bumped the docs build's node-version: '20' → '22' (Node 20 LTS reached EOL ~April 2026); 22 is the current LTS.

Test plan

• All three YAML files parse
• Each new tag's runs.using confirmed node24 (or composite) before pinning
• CI green on this PR (validates checkout@v5 + setup-uv@v7 end-to-end)
• Docs workflow exercised on next docs/** change (or via workflow_dispatch)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR updates the repository’s GitHub Actions pins to versions that are compatible with GitHub’s Node 24 runner runtime transition, preventing Node 20 deprecation warnings and avoiding upcoming breakage. It also updates the docs workflow’s Node version to a newer LTS for the docs build.

Changes:

• Bumped actions/checkout from v4 to v5 in the composite action and CI/docs workflows.
• Bumped astral-sh/setup-uv from v3 to v7 in the composite action and CI workflow.
• Updated docs workflow to use actions/setup-node@v6 with node-version: '22', and bumped Pages actions to upload-pages-artifact@v5 and deploy-pages@v5.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
CHANGELOG.md	Documents the Node 24 compatibility action bumps under Unreleased.
action.yml	Updates the composite action’s checkout and setup-uv steps to Node 24-compatible major tags.
.github/workflows/ci.yml	Updates CI workflow pins for checkout and setup-uv to Node 24-compatible major tags.
.github/workflows/docs.yml	Updates docs workflow pins (Node setup + Pages upload/deploy) and bumps docs build Node version to 22.