docs(release): switch to PR-based release flow

[hakula139]

Summary

Rework the release procedure to land through a PR instead of committing the version bump straight to main and tagging it. The bump and changelog go on a branch, CI runs, the PR is reviewed and merged, and only then is the merged commit tagged. Tagging a reviewed, CI-green commit removes the amend-vs-follow-up-commit dilemma that arises when CI flags something after a direct-to-main tag.

Design decisions

• Tag the merge commit, not a fresh local commit. The previous flow committed chore(release): vX.Y.Z to main and tagged immediately, so a CI failure (e.g. an unknown crate name in the changelog tripping cspell) left a published release on a red commit, forcing either a history-rewriting re-cut or a cosmetically-red follow-up. Gating on a PR makes both unreachable.
• Local checks mirror CI, run before pushing. Folded the full cargo fmt / clippy / test + pnpm lint / spellcheck suite into the procedure so failures surface locally, not in CI.
• Dropped the "If CI fails after the tag is pushed" recovery section. The PR flow makes it unreachable, so documenting recovery would only invite the old path.
• Homebrew formula refresh also goes through a PR, consistent with the no-direct-push rule.

Changes

File	Description
RELEASING.md	PR-based standard release; local check suite; cspell-vs-changelog note; re-cut section trimmed
.claude/skills/release/SKILL.md	Match the PR flow; reminders reordered and reworded; recovery section removed

Test plan

• pnpm lint: 0 errors on both files
• pnpm spellcheck: 0 issues on both files

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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