docs: clarify cognitive memory strategy

[AIPMAndy]

Summary

• explain that DNA Memory is a policy loop for processing memory before storage
• document bounded perception, signal filtering, weighting, cognitive classification, verification, recall feedback, and evolution
• state the biomimetic framing without claiming to reproduce the human brain
• keep the explanation generic and free of personal deployment details

Verification

• python3 scripts/check_public_safety.py: passed
• git diff --check: passed