fix: populate output field in all error ToolResults for AI visibility

[bkrabach]

Summary

• Adds output=error_msg alongside error={"message": error_msg} for all 11 error return paths across grep.py and glob.py
• ToolResult.output is the primary channel the AI reads — when only error={"message": ...} was set, error details were invisible to the AI agent

Context

Same class of bug fixed in amplifier-bundle-lsp PR #3. The pattern applied uniformly:

# BEFORE (error invisible to AI):
return ToolResult(success=False, error={"message": f"Invalid regex pattern: {e}"})

# AFTER (error visible via output):
error_msg = f"Invalid regex pattern: {e}"
return ToolResult(success=False, output=error_msg, error={"message": error_msg})

Test plan

• python_check clean across both files (ruff format, ruff lint, pyright)
• No logic changes — only adds output= parameter to existing returns

🤖 Generated with Amplifier