Polish the new 'Getting Started' Guide

This ticket is a follow-up to the excellent new "Creating Your First App" guide. The goal is to make a few minor formatting adjustments to fully integrate it into the learning portal's rendering engine.

This is a great task to learn about the specifics of how the Neo.mjs documentation portal works.

Tasks:

1. Remove Manual Table of Contents: The file learn/gettingstarted/CreatingYourFirstApp.md currently has a manual Table of Contents at the top. The learning portal generates this automatically from the ## headings, so this section should be removed.

2. Correct Code Block Formatting: The portal requires a special flag on all fenced code blocks to render them correctly.

   • For all shell/bash commands and folder structures, change the fence from shellorplaintextto bash readonly.
   • For all JavaScript code blocks, change the fence from JavaScript to javascript readonly.

3. Add Guide to Navigation: To make the guide appear in the left-hand navigation of the learning portal, add an entry for it in the learn/tree.json file. It should be placed within the "Getting Started" section. The entry should look something like this:

       {"name": "Creating Your First App", "parentId": "GettingStarted", "id": "gettingstarted/CreatingYourFirstApp"}

Verification:

After making the changes, you can see them live by:

1. Running npm run server-start in your terminal.
2. Navigating to the portal app in your browser (usually http://localhost:8080/apps/portal/).
3. Finding the "Creating Your First App" guide in the "Getting Started" section of the side navigation.
4. Verifying that the guide renders correctly, with no manual table of contents and with styled code blocks.