fix: status events don't trigger can-be-merged re-evaluation

[myakove]

Problem

When external services like pre-commit.ci report check results via GitHub's Status API (commit statuses), the webhook server does not process the status event. This means can-be-merged is never re-evaluated when these checks complete.

The server only handles: ping, push, issue_comment, pull_request, pull_request_review, check_run. The status event type is not routed in github_api.py process().

Impact

• can-be-merged check permanently shows Some check runs not started: pre-commit.ci - pr even after pre-commit.ci completes
• PRs cannot be auto-merged when external services use the Status API
• Affects any repository using pre-commit.ci or other Status API-based services

Evidence

From RedHatQE/openshift-cli-installer#897 logs:

cannot be merged: Some check runs not started: pre-commit.ci - pr
no_status_check_runs: ['pre-commit.ci - pr']
branch_required_status_checks: ['can-be-merged', 'verified', 'build-container', 'pre-commit.ci - pr', 'python-module-install', 'tox']

Branch protection correctly includes pre-commit.ci - pr as required, but no status webhook event triggers re-evaluation.

Expected Behavior

When a status event arrives for a PR's head commit:

1. Identify the associated PR
2. Call check_if_can_be_merged() to re-evaluate
3. Update can-be-merged check run accordingly

Deliverables

• Add status event handler in github_api.py process()
• Extract PR from status event payload (commit.sha → find associated PR)
• Trigger check_if_can_be_merged() for the PR
• Add tests for status event handling