Give App Modernization Challenge 1 a sample app and detailed dry-run steps

[gurretl]

Problem

In 03-Azure/01-01-App Innovation/03_GHCPAppModernization, Challenge 1 asks participants to:

• copy the agent, skill and MCP templates "in a target repo", and
• "Dry-run the loop — select your Custom Agent in Copilot Chat and prompt it to modernize a sample."

But no application is available at that point. The PhotoAlbum and PhotoAlbum-Java samples are only forked in Challenge 2, so the final action of Challenge 1 is not executable as written — participants have nothing to point the agent at.

Changes

• Challenge 1 now starts by forking both sample repositories and cloning PhotoAlbum locally, which becomes the explicit target repo for the authored .agent.md, SKILL.md and mcp.json.
• Challenge 1 dry-run is expanded into concrete steps: reload VS Code, select the agent in the picker, use a deliberately open-ended prompt, and verify the Gate 1 / Gate 2 stops. Adds the note that this validates behaviour rather than assessment quality, plus the most common failure cause (editFiles still present in the assessment phase tool list).
• Challenge 2 no longer repeats the fork step; it verifies the forks from Challenge 1 are cloned into the working directory.
• Both walkthroughs (solution-01.md, solution-02.md) are updated to match.

No content is lost — the fork instructions are moved, not removed, and the sample apps are unchanged.

[gurretl]

Closing in favour of a different approach — the dry-run step will be removed from Challenge 1 instead of moving the fork earlier.