docs(dag): record system review findings

[LeXwDeX]

Summary

• record the full DAG system review scope and verification baseline
• document the confirmed summary-publication race fixed by fix(dag): preserve coalesced summary updates #202
• rank architecture findings and explicitly separate unconfirmed robustness risks
• keep Batch C spawnReady optimization closed pending profiling evidence

Verification

• markdown diff check
• repository lint hook: 4849 pre-existing warnings, 0 errors
• repository typecheck hook: 29/29 packages passed