feat: add reusable Node check workflow

npm ci, then npm run <script> for each entry of the scripts input.
PR gate for frontends so Renovate can automerge npm updates.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

README.md

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+# node-check
+
+Reusable Gitea Actions workflow: `npm ci` → `npm run <script>` for each script in a list. Meant as a PR gate for frontend code, for example so Renovate can automerge npm updates.
+
+## Usage
+
+```yaml
+on:
+  pull_request:
+
+jobs:
+  frontend:
+    uses: templates/node-check/.gitea/workflows/node-check.yaml@v1
+    with:
+      working-directory: src/MyApp.Web
+      scripts: "check test build"
+      # node-version: "22"
+```
+
+## Inputs
+
+| Name | Default | Description |
+|---|---|---|
+| `scripts` | (required) | npm scripts separated by spaces. They run in order and the job stops at the first failure. |
+| `working-directory` | `.` | Directory with `package.json` and `package-lock.json` |
+| `node-version` | `22` | Node.js version for `actions/setup-node` |
+
+No secrets. `npm ci` needs a committed `package-lock.json`.
+
+Branch protection: take the exact status-check name from the first PR run. Renaming the workflow `name:` or the job id `check` is a breaking change and needs a new major tag.
+
+## Versioning
+
+Only major tags (`v1`, `v2`, …). Fixes and new optional inputs move the existing tag. Changing or removing inputs, or changing behavior, needs a new major tag.