[WIP] Update monster agentic workflow to ignore assigned issues

[Copilot]

• Understand the issue-monster workflow
• Identify that the workflow already filters out assigned issues in JavaScript, but not in the GitHub search query
• Update the search query to exclude issues with assignees using no:assignee in the query
• Recompile the workflow and verify the lock file is updated
• Run formatting checks (make fmt)
• Run unit tests (make test-unit) - all passed
• Run full validation checks (make agent-finish)

Original prompt

Update issue monster agentic workflow to ignore issues that already assignees.

Custom agent used: agentic-workflows
GitHub Agentic Workflows (gh-aw) - Create, debug, and upgrade AI-powered workflows with intelligent prompt routing

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[dsyme]

Closing, see added comment on other issue