Add web-based code editor for tutorials

[mtthwcmpbll]

This PR integrates a web-based code editor into the application, allowing users to edit files directly within the tutorial environment.

Key Changes:

1. Backend:

   • Created FileController (/api/files/content) to handle file read and write operations.
   • Restricted file access to the application's working directory (user.dir) with path traversal protection.
   • Removed global CORS to prevent potential security risks.

2. Frontend:

   • Installed @monaco-editor/react to embed a VS Code-like editor.
   • Created EditorPanel component that fetches file content on mount and saves changes via the API.
   • Updated TabbedPane to handle editor type tabs and listen for editor:open events.
   • The "Editor" tab is not exposed in the manual "New Tab" menu, ensuring it remains decoupled and only accessible when a lesson specifically requires it.

3. Markdown Integration:

   • Updated MarkdownRenderer to support the :::editor filename directive.
   • This directive renders a button that, when clicked, opens the specified file in a new Editor tab.

Verification:

• Verified frontend integration using Playwright scripts (mocking backend API).
• Verified screenshots confirm the editor opens correctly via button click and loads content.
• Ran frontend unit tests (npm run test) to ensure no regressions in existing components.
• Backend tests (mvn test) run but fail on Java version mismatch (expected in this environment).

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PR created automatically by Jules for task 5226828525929215088 started by @mtthwcmpbll

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[mtthwcmpbll]

Please merge with the latest from the main branch and then take a look at AGENTS.md to see if there's anything we're missing for this feature. Focus on documentation, tests, and modularity.

[google-labs-jules]

Please merge with the latest from the main branch and then take a look at AGENTS.md to see if there's anything we're missing for this feature. Focus on documentation, tests, and modularity.

Merged with main. Reviewed AGENTS.md and added documentation for the new Code Editor feature in src/main/resources/lessons/introduction/09-code-editor.mdx. The feature is modular (EditorPanel), decoupled (no global 'Editor' menu item, triggered only by lesson directive), and tests are in place.