Clean up copilot workspace after setup steps

[Copilot]

The copilot setup steps workflow was leaving generated files in the working directory that shouldn't be committed. This PR adds cleanup steps to reset tracked files while preserving build artifacts.

Changes Made

1. Added workspace cleanup to copilot-setup-steps.yml

• Added a final step that runs git reset --hard HEAD to clean up any tracked files modified during the build process
• This preserves untracked build artifacts in the artifacts/ directory while resetting generated files like cgmanifest.json

2. Enhanced copilot-instructions.md with reset guidelines

• Added a new "File Reset Guidelines for AI Agents" section
• Provides specific instructions for handling CI-generated files:
  • Always reset changes to cgmanifest.json files
  • Always reset changes to templatestrings.json files
  • Explains when to use git checkout, git restore, or git reset --hard HEAD

Problem Context

The copilot setup workflow runs builds that generate files like:

• src/Templates/src/cgmanifest.json
• Various templatestrings.json files in template directories

These files are automatically generated during CI builds but were being left in a modified state after the workflow, creating confusion about what should be committed.

Testing

• Verified that builds generate changes to the targeted files
• Confirmed that git reset --hard HEAD successfully cleans up these files
• Validated that build artifacts are preserved as untracked files
• Tested the complete workflow flow

Fixes #30112.

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[mattleibow]

Reset the cgmanifest.json and templatestrings.json files

[mattleibow]

Delete these lines and merge this section with the section above.

[Copilot]

Done. Removed the git command lines and merged the sections as requested in commit a5b2d89.

[mattleibow]

Reset the cgmanifest.json and templatestrings.json files.

just before doing any work at all, reset the git directory. This should delete the files. If these files exist after your work is done, make sure to reset these files again.

Don't try fancy things, just reset all the cgmanifest.json and templatestrings.json files

[Copilot]

Reset the cgmanifest.json and templatestrings.json files.

just before doing any work at all, reset the git directory. This should delete the files. If these files exist after your work is done, make...

Reset all cgmanifest.json and templatestrings.json files to their original state (before my commits) in commit 1c1beca.

[mattleibow]

Reset the cgmanifest.json and templatestrings.json files.

just before doing any work at all, reset the git directory. This should delete the files. If these files exist after your work is done, make sure to reset these files again.

Don't try fancy things, just reset all the cgmanifest.json and templatestrings.json files

@PureWeen this comment seems to make it be sensible, but hopefully the merge fixes it