Align pnpm patch version in release.yml with devbox.json

[toon-backlog-bot]

Closes #35

Summary

• .github/workflows/release.yml's pnpm/action-setup@v4 step pinned version: 8.15.0, drifting from devbox.json (pnpm_8 @ 8.15.9, fixed in chore: add devbox.json to pin Node 22 + pnpm 8.15.x + Foundry 1.7.1 (+CI) #25). This was the third location with the identical drift, flagged as a follow-up by PR Align pnpm patch version to 8.15.9 across ci.yml and package.json #34 (issue Align pnpm patch version across ci.yml, package.json, and devbox.json (8.15.0 vs 8.15.9 drift) #31) which fixed ci.yml and package.json.
• Changed the single version: 8.15.0 → version: 8.15.9 line in release.yml. No other lines touched — no publish logic, secrets, or triggers changed.
• Added an empty changeset (.changeset/issue-35-release-yml-pnpm-version.md) since this is a CI-config change to no published package.

Verification

grep -n "version: 8.15.9" .github/workflows/release.yml   # → line 26, confirmed
pnpm -r build   # ✅ both packages build
pnpm -r test    # ✅ 130 passed, 2 skipped, 0 failed

Note: pnpm install --no-frozen-lockfile reported pnpm-lock.yaml is already out of sync with packages/swap/package.json on main (pre-existing drift, independent of this change — appears to be what PR #34 addresses for @toon-protocol/{connector,core,sdk} specifiers). I reverted the incidental lockfile changes from that install so this PR's diff stays scoped to the release.yml line the issue calls out; build/test above were verified against the resolved node_modules before reverting the lockfile file itself.

🤖 Generated with Claude Code

[ALLiDoizCode]

Reviewed: single-line pnpm/action-setup@v4 version bump (8.15.0 → 8.15.9) in release.yml to match the pre-existing devbox.json pin, plus a scoped empty changeset. Verified 8.15.9 is devbox.json's actual existing pin, title/body accurately match the diff (5 additions/1 deletion across 2 files), the empty-changeset pattern matches the established sibling-PR convention, and CI (build, devbox-validate) is green. No publish logic, secrets, or triggers touched. No blocking issues.