Clarify how audio becomes trainable and queryable data

Constraint: The guidance had to align with the repo's existing manifest and pgvector templates while staying usable for later industrial ingestion.
Rejected: A purely conceptual note | It would not be actionable for future sessions or data engineering work.
Confidence: high
Scope-risk: narrow
Directive: Keep future dataset onboarding and pgvector ingestion changes anchored on manifest-first contracts and stable song identifiers.
Tested: Relative markdown links for the updated docs were validated locally and repository anchor files were confirmed present.
Not-tested: No model retraining or database ingestion was run in this documentation-only stage.

@@ -60,6 +60,7 @@ flowchart TD
 ### B. 数据与评测
 - [数据规范](./dataset-spec.md)
 - [开放数据工作流](./open-dataset-workflow.md)
+- [训练数据与 pgvector 指南](./training-data-and-pgvector-guide.md)
 - [数据来源与接入](./dataset-sources-and-licensing.md)
 - [工业评测规范](./industrial-benchmark-spec.md)