ci: remove redundant test steps and add coverage artifact uploads

The lint-and-test job was running tests twice:
- 'Backend unit tests' ran tests without coverage
- 'Backend coverage' ran the same tests again with JaCoCo
- 'Frontend unit tests' ran tests without coverage
- 'Frontend coverage' ran the same tests again with v8 coverage

This wasted ~2x test time for no benefit since coverage steps already
run all tests.

- Remove 'Backend unit tests' and 'Frontend unit tests' steps
- Keep only coverage steps (jacocoTestCoverageVerification and test:coverage)
- Add artifact upload steps for both coverage HTML reports:
  - backend-coverage: backend/build/reports/jacoco/test/html/
  - frontend-coverage: frontend/coverage/
  - 7-day retention to avoid storage bloat

Result: lint-and-test job runs faster (no duplicate test runs) and
produces downloadable HTML coverage reports visible in the Forgejo
Actions UI.

.forgejo/workflows/ci.yml

@@ -39,13 +39,6 @@ jobs:
         run: npx vue-tsc --noEmit
         working-directory: frontend
 
-      - name: Frontend unit tests
-        run: npm run test
-        working-directory: frontend
-
-      - name: Backend unit tests
-        run: ./gradlew :backend:test
-
       - name: Backend coverage
         run: ./gradlew :backend:jacocoTestCoverageVerification
 
@@ -53,6 +46,20 @@ jobs:
         run: npm run test:coverage
         working-directory: frontend
 
+      - name: Upload backend coverage report
+        uses: actions/upload-artifact@v4
+        with:
+          name: backend-coverage
+          path: backend/build/reports/jacoco/test/html/
+          retention-days: 7
+
+      - name: Upload frontend coverage report
+        uses: actions/upload-artifact@v4
+        with:
+          name: frontend-coverage
+          path: frontend/coverage/
+          retention-days: 7
+
   e2e:
     name: E2E browser tests
     runs-on: ubuntu-latest