feat: mctf release — tag + goreleaser + release notes from conventional commits #50

Context

Releases are cut by goreleaser on a vX.Y.Z tag (.goreleaser.yaml, docs/RELEASING.md). A mctf release helper would standardize cutting one and drafting notes.

What

mctf release <version>:

• Validates a clean tree + develop/main state.
• Drafts release notes from conventional-commit subjects since the last tag (grouped feat/fix/docs/…).
• Creates the annotated tag and pushes it (triggering the release workflow).

How

• New internal/release (git log parse + notes template) + cmd/release.go.
• Reuse internal/git helpers.
• --dry-run prints the notes + planned tag without pushing.

Acceptance

• mctf release v0.2.0 --dry-run prints grouped notes from commits since the last tag.
• Docs updated; no accidental pushes without confirmation.

Effort

Small–medium.