docs: clarify archived MCP inputs in database audit

[dajiaohuang]

Summary

• distinguish the current core/D&D/CoC repositories from the standalone MCP repositories that were part of the recorded audit baseline
• mark the standalone D&D, CoC, and Narrative MCP repositories as archived historical evidence only
• point each historical repository entry to its current vertical domain authority and exclude it from release inputs or compatibility fallbacks

Validation

• git diff --check
• focused full-diff review
• staged secret-pattern scan

Related architecture alignment: SagaSmithAI/SagaSmith-service#10, SagaSmithAI/.github#5, SagaSmithAI/SagaSmithAI.github.io#5