feat: fan out monthly optimization tasks

[Pigbibi]

Summary

• add repo-scoped monthly optimization task fanout issue creation
• wire planner workflow to create task issues for CryptoLeaderRotation and attempt cross-repo fanout safely
• append fanout results to the workflow step summary

Testing

• python3 -m unittest tests/test_build_ai_review_payload.py tests/test_build_monthly_optimization_plan.py tests/test_post_monthly_optimization_issue.py tests/test_fanout_monthly_optimization_tasks.py tests/test_monthly_optimization_planner_workflow_config.py
• uvx ruff check scripts tests
• ruby -e 'require "yaml"; Dir[".github/workflows/*.yml"].each { |f| YAML.load_file(f) }; puts "yaml ok"'