Notify failures even when the manifest is broken

The existing GitHub notice runs on a push to main after the manifest parses. The Forgejo migration must also report PR check failures, invalid or missing manifests, publication failures, and recovery to the existing Project channel. Resolve that channel independently from trusted repository metadata. Include the commit, run link and outcome, with durable retry and duplicate suppression. Document content and credentials stay out of notices.

Notification failure must not turn a failed gate into success. Exercise a malformed manifest and a workflow that cannot start, then confirm the operator receives the failure through the trusted reporting path.