ci: add dependency-review-action for PR vulnerability scanning

Scans pull requests for vulnerabilities introduced by dependency
changes. Works with pnpm lockfiles. Posts a summary comment on PR
when vulnerabilities are found at moderate severity or higher.

Note: For fork PRs, the comment may not post due to permission
restrictions, but the check will still fail.

Author: mroderick

.github/workflows/dependency-review.yml

@@ -0,0 +1,22 @@
+name: Dependency Review
+
+on:
+  pull_request:
+    branches: [main]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  dependency-review:
+    name: Dependency Review
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - uses: actions/dependency-review-action@a6993e2c61fd5dc440b409aa1d6904921c5e1894 # v4.3.5
+        with:
+          comment-summary-in-pr: on-failure
+          fail-on-severity: moderate