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/navigation.cy.js

@@ -0,0 +1,57 @@
+import { loginWithFixtures, setupApiIntercepts } from '../support/intercept';
+
+describe('Navigation and Routing', () => {
+  it('redirects / to /files when logged in', () => {
+    loginWithFixtures();
+    cy.visit('/');
+    cy.url().should('include', '/files');
+  });
+
+  it('shows 404 page for unknown routes', () => {
+    loginWithFixtures();
+    cy.visit('/nonexistent-page');
+    cy.contains('404').should('exist');
+  });
+
+  it('navbar shows correct view name', () => {
+    loginWithFixtures();
+    cy.visit('/files');
+    cy.wait('@getFiles');
+    cy.get('#nav_bar').should('exist');
+    cy.get('#nav_bar h2').should('contain', 'FILES');
+  });
+
+  it('navbar shows back arrow on non-files pages', () => {
+    loginWithFixtures();
+    cy.visit('/discover/log/1/map');
+    // Back arrow should be visible on discover pages
+    cy.get('#backPage').should('exist');
+  });
+
+  it('navbar tabs are clickable on discover page', () => {
+    loginWithFixtures();
+    cy.visit('/discover/log/1/map');
+    // Discover navbar should show MAP, CONFORMANCE, PERFORMANCE tabs
+    cy.contains('.nav-item', 'MAP').should('exist');
+    cy.contains('.nav-item', 'CONFORMANCE').should('exist');
+    cy.contains('.nav-item', 'PERFORMANCE').should('exist');
+
+    // Click CONFORMANCE tab
+    cy.contains('.nav-item', 'CONFORMANCE').click();
+    cy.url().should('include', '/conformance');
+
+    // Click PERFORMANCE tab
+    cy.contains('.nav-item', 'PERFORMANCE').click();
+    cy.url().should('include', '/performance');
+
+    // Click MAP tab to go back
+    cy.contains('.nav-item', 'MAP').click();
+    cy.url().should('include', '/map');
+  });
+
+  it('login page is accessible at /login', () => {
+    setupApiIntercepts();
+    cy.visit('/login');
+    cy.get('h2').should('contain', 'LOGIN');
+  });
+});