feat(docs): Populate Developer Portal with comprehensive documentation framework (#35217)

Co-authored-by: Claude <noreply@anthropic.com>

docs/developer_portal/testing/e2e-testing.md

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+---
+title: End-to-End Testing
+sidebar_position: 4
+---
+
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+  http://www.apache.org/licenses/LICENSE-2.0
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+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
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+-->
+
+# End-to-End Testing
+
+🚧 **Coming Soon** 🚧
+
+Guide for writing and running end-to-end tests using Playwright and Cypress.
+
+## Topics to be covered:
+
+### Playwright (Recommended)
+- Setting up Playwright environment
+- Writing reliable E2E tests
+- Page Object Model pattern
+- Handling async operations
+- Cross-browser testing
+- Visual regression testing
+- Debugging with Playwright Inspector
+- CI/CD integration
+
+### Cypress (Deprecated)
+- Legacy Cypress test maintenance
+- Migration to Playwright
+- Running existing Cypress tests
+
+## Quick Commands
+
+### Playwright
+```bash
+# Run all Playwright tests
+npm run playwright:test
+
+# Run in headed mode (see browser)
+npm run playwright:headed
+
+# Run specific test file
+npx playwright test tests/auth/login.spec.ts
+
+# Debug specific test
+npm run playwright:debug tests/auth/login.spec.ts
+
+# Open Playwright UI
+npm run playwright:ui
+```
+
+### Cypress (Deprecated)
+```bash
+# Run Cypress tests
+cd superset-frontend/cypress-base
+npm run cypress-run-chrome
+
+# Open Cypress UI
+npm run cypress-debug
+```
+
+---
+
+*This documentation is under active development. Check back soon for updates!*