Fix auto-merge: compare required checks by app_id instead of app name

[hiroshinishio]

Summary

• Fix critical bug: auto-merge handler compared check suite app names (e.g. "CircleCI Checks") against required status check context strings (e.g. "build_deploy_development_workflow"), which never matched. Now compares by app_id available in both data sources.
• Add app_ids: set[int] | None to StatusChecksResult dataclass, extracted from branch protection API response
• Add MergeableState Literal type in its own module, used in PullRequest TypedDict and BLOCKED_STATE_REASONS
• Replace vague not in condition with explicit in BLOCKED_STATE_REASONS check
• Improve all log messages to state consequences ("returning because...", "proceeding to merge because...")
• Delete unused get_check_runs module
• 50 tests covering real repo scenarios (website PRs GitAuto: Low Test Coverage: services/github/comments/get_comments.py #809-Low Test Coverage: services/slack/slack.py #811, Foxquilt with CircleCI app_id=18001)

Social Media Post (GitAuto)

Auto-merge bug fix: required check comparison now uses app_id

• Fixed a bug where auto-merge compared app names against check context strings, which never matched
• Required status checks now correctly matched by app_id from branch protection API
• Added 50 tests covering real customer scenarios including CircleCI and GitHub Actions