AX-2134: unify release trigger on version-file diff

[YoniMelki]

Summary

• Switch release.yml from tag-push to push-to-main, comparing package.json against the latest strict vX.Y.Z tag.
• Bump 0.1.0 → 0.1.1 so merge is a real release (tag v0.1.0 already exists).
• PR-time semver shape check in ci.yml; steering / pin-sync / skills drift checks unchanged in behavior.
• Concurrency added; checkout/setup-node bumped to v5.

Part of AX-2134.

Landing

Merging cuts v0.1.1 (no zip — the tag is the Kiro install target). After that, every merge must bump package.json or Release fails by design.

Open skills-sync PRs #5, #6, and #8 already bump to 0.1.1. After this lands they must rebase and bump to 0.1.2+ or Release will fail with "already released".

Test plan

• Confirm merge creates GitHub Release v0.1.1 with no asset.
• Confirm CI still fails on a non-X.Y.Z version.
• Confirm steering / pin-sync / vendoring drift steps still run on a real release.
• Rebase/re-bump skills-sync PRs [patch] chore: sync skills to v0.25.0 #5/[patch] chore: sync skills to v0.28.0 #6/[patch] chore: sync skills to v0.29.0 #8 before merging them.