fix: split coverage into separate backend and frontend steps

- Backend coverage runs from repo root where gradlew lives
- Frontend coverage runs from frontend/ with working-directory
- No cd tricks that break relative paths

.forgejo/workflows/ci.yml

@@ -48,12 +48,12 @@ jobs:
       - name: Backend unit tests
         run: ./gradlew :backend:test
 
-      - name: Coverage verification
-        run: |
-          cd ..
-          ./gradlew :backend:jacocoTestCoverageVerification
-          cd frontend
-          npm run test:coverage
+      - name: Backend coverage
+        run: ./gradlew :backend:jacocoTestCoverageVerification
+
+      - name: Frontend coverage
+        run: npm run test:coverage
+        working-directory: frontend
 
   e2e:
     name: E2E browser tests