Update mcp image gallery lab

[edinc]

This pull request updates the docs/hands-on/gh-gallery-mcp.md file with improvements to the setup instructions and the example used for analyzing a mockup in GitHub Copilot Chat. These changes enhance clarity and ensure the instructions are aligned with the current repository structure and assets.

Setup Instructions Update:

• Added a step to enable Issues in the forked repository to ensure users can experiment with the code and create issues as part of the hands-on exercise.

Example Mockup Update:

• Replaced the example image file img_gallery_prompt.jpg with crazy_mockup.png from the ghcp-mcp/html/mockup directory, and updated the instructions to reflect this change. This ensures the example aligns with the repository's current structure.## Purpose

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[x] Documentation content changes
[ ] Other... Please describe:

How to Test

• Get the code

git clone [repo-address]
cd [repo-name]
git checkout [branch-name]
npm install