fix(e2e): Fix 12 failing E2E tests - DataTable reactivity and selector issues

- Fix DataTable reactivity: use $derived with getters for data/columns props
- Fix auth.spec.js: open user dropdown before clicking Logout button
- Fix dashboard.spec.ts: scope selectors to layout-content, use exact matches
- Fix layout.spec.ts: clear localStorage before breakpoint tests, wait for focus
- Fix projects/team-members.spec.ts: wait for table rows to be visible

Root causes:
1. DataTable options object captured initial empty array, not reactive updates
2. Selectors matched multiple elements (sidebar, user menu, main content)
3. Dropdown menus need to be opened before clicking items
4. Keyboard shortcuts need element focus

All 94 tests now pass (47 chromium + 47 firefox)

frontend/tests/e2e/auth.spec.js

@@ -159,8 +159,9 @@ test.describe('Authentication E2E', () => {
       await page.click('button[type="submit"]');
       await page.waitForURL('/dashboard');
       
-      // Click logout
-      await page.click('text=Logout');
+      // Open user menu dropdown first, then click logout
+      await page.click('[data-testid="user-menu"] button');
+      await page.click('[data-testid="user-menu"] button:has-text("Logout")');
       
       // Should redirect to login
       await page.waitForURL('/login');