ci: fix release-reusable git identity and add manual dispatch - #25

What & why

The first release-reusable run (from #24) failed at git tag -a with fatal: empty ident name — the runner has no git user configured, so annotated tags can't be created. The version math ran fine (Releasing v1.0.0 (previous v0.0.0)) and it failed before any tag or push, so nothing partial landed.

This:

• sets the github-actions[bot] git identity before tagging;
• adds workflow_dispatch with a bump (patch/minor/major) input so a release can be cut on demand — needed right now because this fix commit only touches release-reusable.yml, which isn't a reusable-* trigger path, so it won't auto-fire;
• factors the bump level into one variable shared by the push and dispatch paths.

After merge I'll dispatch it with bump: major to cut the inaugural v1.0.0 (+ v1), then re-pin the forks onto that tag.

Type of change

• fix / feat / perf — consumer-facing
• deps — dependency update (add the security label if it fixes a CVE)
• chore / ci / build / docs / test / refactor — maintenance

Checklist

• Commits follow Conventional Commits (commitlint passes)
• npm test passes on Node 20 / 22 / 24 — workflow-only change, no package surface
• No new runtime dependency (or its addition is justified below)
• Dev tree kept lean (prefer built-in node:test over new runners)

Generated by Claude Code