ci(unit-tests): add early grep check for banned vi.mock pdfjs-dist pattern

Adds a static grep step that runs after Lint and before the test suite.
Fails in ~1 s if any file under frontend/src/ contains the banned
vi.mock('pdfjs-dist' pattern, catching the regression before Playwright
spins up. Belt-and-suspenders with the ESLint rule (ADR 012).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -36,6 +36,14 @@ jobs:
         run: npm run lint
         working-directory: frontend
 
+      - name: Assert no banned vi.mock patterns
+        shell: bash
+        run: |
+          if grep -rF "vi.mock('pdfjs-dist'" frontend/src/; then
+            echo "FAIL: banned vi.mock('pdfjs-dist') pattern found — see ADR 012. Use the libLoader prop injection pattern instead."
+            exit 1
+          fi
+
       - name: Run unit and component tests with coverage
         shell: bash
         run: |