chore(ci): add zizmor workflow for github actions security analysis (#471)

Adds [zizmor](https://github.com/zizmorcore/zizmor) to audit GitHub
Actions workflows for security issues. Runs on push to main and on PRs
that change `.github/workflows/**`. Fails CI on any finding.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Mostly CI/workflow hardening, but it also changes release automation
(`postversion.sh`) and workflow permissions/credentials behavior, which
could break tagging/publishing if misconfigured.
> 
> **Overview**
> Adds a new `zizmor` workflow that runs on PRs/pushes touching
`.github/workflows/**` to security-audit workflows.
> 
> Hardens existing workflows by defaulting to least-privilege
`permissions`, setting `actions/checkout` to `persist-credentials:
false`, and adjusting related behavior (e.g., `scripts/postversion.sh`
now runs `gh auth setup-git` so `git push` still works; `ci.yml`
disables `mise-action` caching; `test.yml` avoids interpolating
`steps.bad.outcome` inside a shell string by passing it via env).
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
d878aee510. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/postversion.sh

@@ -4,6 +4,11 @@ set -euxo pipefail
 VERSION=$(jq -r .version package.json)
 MAJOR_VERSION=$(echo "$VERSION" | cut -d. -f1)
 
+# Configure git to use gh's credential helper. The checkout step uses
+# persist-credentials: false (per zizmor's artipacked audit), so the
+# token isn't written to .git/config and raw `git push` would 403.
+gh auth setup-git
+
 # create the version tag (allow it to fail if it already exists)
 git tag "v$VERSION" || echo "Tag v$VERSION already exists locally"