feat: add auto optimization draft pr workflow

[Pigbibi]

Summary

• add a repo-local workflow that turns monthly-optimization-task issues into draft PRs for low-risk auto-pr-safe tasks
• add parser utilities and tests for selecting eligible issue actions and preparing PR metadata
• allow CI to be dispatched manually so automation branches can still be validated

Testing

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