[WIP] Fix issue download script to use GitHub MCP tools

[Copilot]

Fix Chroma Issue Indexer Workflow

• Understand the problem from failed workflow logs
• Update chroma-issue-indexer.md to use GitHub MCP tools instead of Python
• Ensure "issues" collection is created before adding documents
• Implement batch processing (5 issues at a time)
• Recompile workflow and verify changes
• Test the updated workflow
• Validate changes with make agent-finish

Original prompt

Reference: https://github.com/githubnext/gh-aw/actions/runs/21285426089/job/61265295156

Debug script:

• use GitHub MCP tools, not Python to get issue information
• download up to 5 issues at a time
• ensure "issues" collection already exists in chroma

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