[eric] lint: wire structlint CI job

.github/workflows/lint.yml

@@ -0,0 +1,21 @@
+name: Lint
+
+on:
+  pull_request:
+    branches: [main]
+
+jobs:
+  structlint:
+    name: Structure lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      # lint.py imports watchfiles at module load; vulture backs the dead-code check.
+      - run: pip install watchfiles vulture==2.16
+
+      - run: python3 linter/lint.py --root .