Implement delegated sync and full-sync-risk receipts

[mdheller]

Purpose

Implement sourceos-syncd support for delegated sync accountability, anchored to SourceOS spec PR #96:

SourceOS-Linux/sourceos-spec#96

Required receipts

• SyncCycleReceipt
• DelegatedIOReceipt
• FullSyncRiskReceipt
• CloudObjectTransferReceipt
• SchedulerReceipt
• TemporaryArtifactLifecycleReceipt

Required fields

• sync root;
• object IDs;
• actor chain;
• direction;
• batch size;
• scheduler kind;
• throttle/retry/backoff;
• full-sync/checkpoint state;
• local metadata DB writes;
• cloud/fog object transfer bytes;
• logical vs physical vs clone/reflink vs dirty-memory bytes.

Acceptance criteria

• A sync incident can explain origin actor, requesting actor, executing service, object namespace, DB writes, object transfers, and cleanup/staging transitions.
• Full-sync or reindex risk is emitted before expensive work starts when possible.
• Tests reject delegated sync events without a complete actor chain.