feat: implement E2E testing workflow and enhance XML syntax editor

- Added a new GitHub Actions workflow for end-to-end (E2E) testing, including setup for Node.js, Playwright, and server initialization.
- Introduced a setup script for E2E test fixtures to create necessary directories and files.
- Integrated CodeMirror for XML syntax editing in the XmlSyntaxEditor component, improving code highlighting and editing experience.
- Updated package dependencies in package.json and package-lock.json to include new libraries for XML handling and theming.
- Refactored various components for improved readability and consistency, including the sidebar and file browser dialog.
- Added tests for spec editor persistence to ensure data integrity across sessions.

apps/app/playwright.config.ts

@@ -30,6 +30,10 @@ export default defineConfig({
           url: `http://localhost:${port}`,
           reuseExistingServer: !process.env.CI,
           timeout: 120000,
+          env: {
+            ...process.env,
+            NEXT_PUBLIC_SKIP_SETUP: "true",
+          },
         },
       }),
 });