Add setup handler to auto-create coverage workflow PRs

[hiroshinishio]

Summary

• New setup_handler that runs on install: detects repo language from root files, creates a PR with the appropriate GitHub Actions coverage workflow YAML
• Creates PR first (like other handlers), runs Claude agent loop, closes PR + deletes branch if agent doesn't complete
• Added close_pull_request API helper for cleanup
• Moved VERIFY_TASK_IS_COMPLETE into _TOOLS_BASE so all handlers (issues, PRs, setup) use it
• Fixed verify_task_is_complete bug: no PR file changes now returns success (setup handler may determine no workflow is needed)
• Added FastAPI endpoint at /api/{owner}/{repo}/setup_coverage_workflow
• Full observability: usage tracking, slack notifications, trigger/PR metadata
• Auto-triggers on install when a single repo is added
• Fixed test_clone_and_install and test_process_repositories tests broken by function signature and import changes

Social Media Post (GitAuto)

GitAuto's coverage dashboard shows your files after install, but if you don't have a CI workflow that runs tests and uploads coverage data, the percentages and charts stay empty. That setup step is where most users got stuck. Now on install, GitAuto detects your language and opens a PR with the right CI workflow. Merge it and coverage data starts flowing.

Social Media Post (Wes)

After installing GitAuto, the coverage dashboard shows your files but coverage percentages and charts are empty if you don't already have a CI workflow that runs tests and uploads an LCOV report. Setting that up is where most users drop off - honestly I would too. So we automated it. On install, we detect the language from your repo and open a PR with the right CI workflow. Merge it and coverage data starts flowing.