Automate release publishing end-to-end

[0xisk]

🧐 Motivation

The release flow is mostly manual and brittle. Cutting v0.1.0 required manually creating the GitHub Release/tag, and a failed build meant manually deleting and recreating the tag/release to retry. We should automate it so a release is a single deterministic action.

📝 Details

Automate so that merging the version-bump PR to main (from a release-v* branch) drives the rest:

• Auto-create the GitHub Release + tag v<version> from contracts/package.json on merge, which fires the existing release.yml publish job. No manual release creation.
• Make retries safe/idempotent (re-running shouldn't need manual tag deletion).

Out of scope / tracked separately:

• prepare-release.yml needs the GH_APP_ID var + GH_APP_PRIVATE_KEY secret configured (the version-bump step currently fails without them).
• release.yml missing the Compact compiler install — fixed in ci(release): install Compact compiler before build #550.

✅ Acceptance

• Merging a release-v* bump publishes to npm with no manual GitHub UI steps.
• A failed publish can be retried without manual tag/release surgery.