feat: skip all CI checks and comment once when PR has merge conflicts #1208

Problem

When a pushed PR has merge conflicts, the webhook server still queues and runs all CI checks (tox, pre-commit, container build, python module install, conventional-title, security checks, custom checks). Running CI against an unmergeable state wastes compute, and the author gets no clear signal that they need to resolve conflicts.

Accepted design

Every webhook delivery that definitively detects merge conflicts posts a conflict notification comment. Repeated comments are intentional audit/tracking events showing that pushes continue while conflicts remain. No comment-marker lookup or deduplication is performed.

This explicitly resolves the Qodo repeated/concurrent-comment finding: repeated and concurrent conflict notifications are an accepted, documented requirement rather than a defect.

Behavior

• On push/synchronize, determine conflict state via pull_request.mergeable is False (existing detection in label_pull_request_by_merge_state).
• If the PR has conflicts:
  • Add the has-conflicts label (existing behavior).
  • Skip all CI checks — do not queue or run any of them.
  • Post a conflict notification comment for every webhook delivery that definitively detects the conflicts, explaining why CI did not run and that resolving the conflicts (rebase/merge) will re-trigger checks on the next push.
• When conflicts clear, the has-conflicts label is removed (existing behavior) and CI runs normally on the next push. If conflicts later reappear, conflict notification comments resume for each qualifying webhook delivery.

Done

• process_opened_or_synchronize_pull_request skips all CI check queueing and runner tasks when pull_request.mergeable is False
• has-conflicts label added when conflicts are detected (existing transition logic reused)
• A conflict notification comment is posted for every webhook delivery that definitively detects conflicts
• No comment-marker lookup or comment deduplication is performed
• Comment text explains CI was skipped due to merge conflicts and that resolving them re-triggers checks
• Unit tests cover conflicting deliveries (including repeated/concurrent deliveries), no-conflict pushes, and normal CI behavior after conflicts clear
• docs/ regenerated via docsfy (or deferred to a follow-up issue if docsfy is unavailable)

Assisted-by: PI (gpt-5.6-luna)