fix(scan): recover durable scans and library maintenance

[Lowband21]

Summary

• make PostgreSQL job and maintenance state authoritative across broadcast lag, restarts, lease expiry, and terminalization
• repair scheduler, merge, watcher handoff, and immediate-completion enrollment races that could leave scans permanently stuck
• rotate root discovery beyond the first 512 entries, expose deferred/truncated discovery metrics, and prefer polling for detected CIFS/NFS mounts
• make library delete, reset, and clear-all-data work end to end, including ordered intelligence_artifact_sources cleanup and idempotent reset recovery
• add regressions for more than 256 event bursts, lag recovery, enqueue-time completion, paths beyond entry 512, network filesystems, scan status, and destructive dashboard actions

[cloudflare-workers-and-pages]

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