ci(openapi): add version-check workflow

Author: Codex

.github/workflows/openapi-version-check.yml

@@ -0,0 +1,34 @@
+name: OpenAPI Version Check
+
+on:
+  pull_request:
+    paths:
+      - public/openapi.json
+      - CHANGELOG.md
+      - scripts/check-openapi-version.mjs
+      - .github/workflows/openapi-version-check.yml
+
+permissions:
+  contents: read
+
+jobs:
+  openapi-version:
+    name: OpenAPI version bump
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          fetch-depth: 0
+
+      - uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
+        with:
+          node-version: '22'
+
+      - name: Load base OpenAPI spec
+        run: |
+          git fetch --no-tags --depth=1 origin "${{ github.base_ref }}"
+          git show "origin/${{ github.base_ref }}:public/openapi.json" > /tmp/openapi.base.json || echo '{}' > /tmp/openapi.base.json
+
+      - name: Check OpenAPI version policy
+        run: node scripts/check-openapi-version.mjs /tmp/openapi.base.json public/openapi.json