feat(ci): automatic release versioning with rc support

[Enubia]

Summary

• New .github/scripts/next-version.sh computes the next release tag from conventional commits since the last stable tag: always at least a patch bump, feat: escalates to minor, !-subjects or BREAKING CHANGE: footers to major; --rc appends an auto-incrementing -rc.N; covered by a 16-assertion scratch-repo test suite
• The Release workflow now auto-detects the version via a determine-version job (the old version input remains as an optional override), adds a release-candidate checkbox that marks the draft release as prerelease, fails fast on tag collisions, and queues concurrent dispatches
• Quick Checks gains a pr-title job (amannn/action-semantic-pull-request) so squash-merge commit subjects stay conventional; CONTRIBUTING.md documents the new title requirement

Design spec and implementation plan included under docs/superpowers/.

Test Plan

• bash .github/scripts/next-version.test.sh — 16/16 assertions pass
• go test ./... — all green
• After merge: dispatch Release with release-candidate checked and version empty; expect a draft prerelease tagged v4.3.0-rc.1 and the version shown in the job summary
• After merge: open a test PR with a non-conventional title, confirm pr-title fails, rename to chore: test, confirm it passes

🤖 Generated with Claude Code

[cloudflare-workers-and-pages]

Deploying ghost-chat with    Cloudflare Pages

Latest commit:	7ef6217
Status:	✅  Deploy successful!
Preview URL:	https://bb11b149.ghost-chat-4c1.pages.dev
Branch Preview URL:	https://feat-auto-release-versioning.ghost-chat-4c1.pages.dev

View logs