Mark prerelease tags as prereleases on the GitHub release

[alexeyzimarev]

The Create GitHub Release step in .github/workflows/release.yml (softprops/action-gh-release) sets neither prerelease nor make_latest, so a prerelease tag is published as a normal release and takes the Latest badge.

Observed after cutting v0.12.0-beta.1 on 2026-09-08:

$ gh release view v0.12.0-beta.1 --json isPrerelease --jq .isPrerelease
false
$ gh release list --limit 2
v0.12.0-beta.1   Latest   2026-09-08
v0.11.40                  2026-09-08

npm is unaffected: scripts/npm-dist-tag.sh already routes a prerelease to the beta dist-tag, and kcap update reads dist-tags, not GitHub releases. The damage is limited to GitHub itself: the releases page and releases/latest point at the beta instead of the stable release.

Fix: derive the flag from the tag the same way the npm dist-tag does (a hyphen in the version core) and keep prereleases off the Latest badge:

      - name: Create GitHub Release
        uses: softprops/action-gh-release@v3
        with:
          files: release-artifacts/*
          generate_release_notes: true
          prerelease: ${{ contains(github.ref_name, '-') }}
          make_latest: ${{ !contains(github.ref_name, '-') }}

v0.12.0-beta.1 itself can be corrected by hand (gh release edit v0.12.0-beta.1 --prerelease, then gh release edit v0.11.40 --latest).

[linear-code]

AI-2600