Add workflow to auto-build dist on Dependabot PRs (#782)

When Dependabot bumps dependencies in package.json, this workflow
automatically runs `npm run all` to rebuild the dist folder and commits
the changes back to the PR.

This ensures the compiled JavaScript in `dist/` stays in sync with
dependency updates.

**How it works:**
1. Triggers on PRs opened by `dependabot[bot]`
2. Runs `npm ci` and `npm run all` (build, check, package, test)
3. Commits any changes to `dist/` back to the PR branch

Uses `stefanzweifel/git-auto-commit-action` for the commit step.

.github/workflows/dependabot-build.yml

@@ -0,0 +1,39 @@
+name: Dependabot Build
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: write
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: github.event.sender.login == 'dependabot[bot]' && github.event.sender.type == 'Bot'
+    steps:
+      - name: Checkout PR branch
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          ref: ${{ github.head_ref }}
+          persist-credentials: false
+
+      - name: Setup Node.js
+        uses: actions/setup-node@6044e13b5dc448c55e2357c09f80417699197238 # v6.2.0
+        with:
+          node-version-file: .nvmrc
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build and test
+        run: npm run all
+
+      - name: Commit built dist
+        uses: stefanzweifel/git-auto-commit-action@b863ae1933cb653a53c021fe36dbb774e1fb9403 # v5
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          commit_message: "Build dist for Dependabot update"
+          file_pattern: dist/