docs: add model and retention record templates

[Hinotoi-agent]

Summary

• add an informative Model Change and Drift Record Template appendix for documenting model changes, behavioral comparisons, drift detections, re-attestation decisions, and rollback evidence
• add an informative Data Retention and Disposal Record Template appendix for documenting retention decisions, secure deletion, disposal verification, exceptions, and customer deletion requests
• link both templates from the standard overview, getting-started document, and related AR/TP requirements

Affected sections / requirement IDs

• standard/appendix/Model_Change_and_Drift_Record_Template.md
• standard/appendix/Data_Retention_and_Disposal_Record_Template.md
• standard/README.md
• standard/Getting_Started.md
• standard/5_Auditability/README.md
• standard/7_Supply_Chain_Trust/README.md
• Supports existing requirements: APTS-AR-019, APTS-TP-002, APTS-TP-015, APTS-TP-016, APTS-TP-021, APTS-TP-022

Validation

• git diff --check
• python3 scripts/validate_markdown_tables.py
• python3 scripts/check_internal_markdown_links.py
• python3 scripts/validate_cross_references.py
• python3 scripts/check_generated_artifacts.py
• python3 scripts/validate_yaml.py

Notes

• These appendices are informative and do not add or modify normative APTS requirements.
• I reviewed open issues/PRs and did not find an overlapping open item for these two record templates.
• Drafted with AI assistance; I reviewed the changes for accuracy, consistency with the standard, and style-guide compliance.

[jinsonvarghese]

Reviewed the two new templates and all cross-references against the standard. LGTM, approving.