test(frontend): add jsdom tests for the file manager

Sobe web/index.html + web/js/app.js de verdade em jsdom, intercepta a API
e cobre arrastar-e-soltar entre pastas, mover/renomear/excluir, filtros,
busca e preview. CI passa a rodar npm ci && npm test.

.github/workflows/ci.yml

@@ -16,7 +16,8 @@ jobs:
           cache: true
       - uses: actions/setup-node@v4.1.0
         with:
-          node-version: 20
+          node-version: 22
+          cache: npm
       - name: gofmt
         run: test -z "$(gofmt -l internal cmd)"
       - name: go vet
@@ -25,3 +26,5 @@ jobs:
         run: go test -race ./...
       - name: frontend syntax
         run: node --check web/js/app.js
+      - name: frontend tests
+        run: npm ci && npm test