feat: improved e2e tests

frontend/app/cypress/PITFALLS.md

@@ -0,0 +1,29 @@
+# A list of (possibly) common pitfalls
+
+## The component is not updating
+
+### Calling Cypress invoke will not trigger change detection
+
+Rewrite
+
+```typescript
+cy.get('component-selector').component().invoke('someFunction');
+```
+
+Into
+
+```typescript
+cy.get('component-selector')
+  .component()
+  .runInsideAngular(component => component.someFunction());
+```
+
+## The backend is unreachable
+
+See `BACKEND.md`, direct calls to backend are prohibited.
+
+## The search page doesn't work
+
+Run `cy.patchSearchPage()` after visiting the search page.
+It set the due time to zero so that the component
+won't wait for someone to type more.