feedback5 R6: run lint, import check and typecheck in CI

One extra Ubuntu job. The existing test matrix is unchanged. Lint warnings are allowed.

.github/workflows/ci.yml

@@ -66,3 +66,29 @@ jobs:
           curl -fsS -o /dev/null http://127.0.0.1:3000/vendor/pixi.min.js
           node tools/doctor.mjs || true
           kill $pid || true
+
+  # Separate from the test matrix so lint / types / import boundaries run once, not four times.
+  # Lint warnings do not fail the job (npm run lint does not pass --max-warnings=0).
+  tooling:
+    name: tooling (lint, imports, typecheck)
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@v7
+
+      - uses: actions/setup-node@v7
+        with:
+          node-version: 22
+          cache: npm
+
+      - name: Install (npm ci → postinstall copies public/vendor)
+        run: npm ci --no-audit --no-fund
+
+      - name: Lint (warnings allowed)
+        run: npm run lint
+
+      - name: Import boundaries
+        run: npm run check:imports
+
+      - name: Typecheck
+        run: npm run typecheck