Add Cypress E2E tests with fixture-based API mocking for UI regression protection

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

cypress/e2e/files.cy.js

@@ -0,0 +1,55 @@
+import { loginWithFixtures } from '../support/intercept';
+
+describe('Files Page', () => {
+  beforeEach(() => {
+    loginWithFixtures();
+    cy.visit('/files');
+  });
+
+  it('displays the file list after login', () => {
+    cy.wait('@getFiles');
+    cy.contains('h2', 'All Files').should('exist');
+    // Should display file names from fixture
+    cy.contains('sample-process.xes').should('exist');
+    cy.contains('filtered-sample').should('exist');
+    cy.contains('production-log.csv').should('exist');
+  });
+
+  it('shows Recently Used section', () => {
+    cy.wait('@getFiles');
+    cy.contains('h2', 'Recently Used').should('exist');
+  });
+
+  it('switches to DISCOVER tab', () => {
+    cy.wait('@getFiles');
+    cy.contains('.nav-item', 'DISCOVER').click();
+    // DISCOVER tab shows filtered file types
+    cy.contains('h2', 'All Files').should('exist');
+  });
+
+  it('switches to COMPARE tab and shows drag zones', () => {
+    cy.wait('@getFiles');
+    cy.contains('.nav-item', 'COMPARE').click();
+    cy.contains('Performance Comparison').should('exist');
+    cy.contains('Drag and drop a file here').should('exist');
+  });
+
+  it('shows Import button on FILES tab', () => {
+    cy.wait('@getFiles');
+    cy.get('#import_btn').should('contain', 'Import');
+  });
+
+  it('can switch between list and grid view', () => {
+    cy.wait('@getFiles');
+    // DataTable (list view) should be visible by default
+    cy.get('table').should('exist');
+  });
+
+  it('double-click file navigates to discover page', () => {
+    cy.wait('@getFiles');
+    // Double-click the first file row in the table
+    // The actual route depends on file type (log→map, log-check→conformance, etc.)
+    cy.get('table tbody tr').first().dblclick();
+    cy.url().should('include', '/discover');
+  });
+});