docs: add AI data deletion propagation gates

[catcherintheroad-hub]

Created from review issue: #1382

Summary

• Add deletion propagation evidence gates for AI-derived privacy stores.
• Require source-to-derived mapping across embeddings, vector indexes, logs, training snapshots, model artifacts, analytics exports, backups, provider retention, and legal holds.
• Add report output fields and edge-case fixtures for DSAR primary-only deletion, vector residuals, training snapshot consent withdrawal, and complete propagation ledgers.

Validation

• git diff --check
• Markdown fence/non-ASCII sanity check
• Reference URL checks for GDPR Article 17, NIST AI RMF, and OWASP LLM Top 10