Add C5.2.10: AI pipeline data classification taxonomy

[emmanuelgjr]

Summary

• Adds C5.2.10 (Level 2): requires a documented data classification taxonomy covering AI-specific data types (embeddings, model weights, prompt templates, RAG context assemblies, fine-tuning datasets, agent tool schemas) with assets labeled accordingly
• Adds cross-reference note to ASVS v5 14.1.1 and explains the prerequisite relationship with C5.2.4 and C5.2.7

Rationale

C5.2.4 requires classification labels to propagate to derived resources and C5.2.7 requires policies to evaluate resource classification, but no existing control requires the classification scheme itself to be defined for AI-specific data types. ASVS 14.1.1 covers general data classification but does not enumerate AI-specific data types. This fills the prerequisite gap.

See discussion in #671 for full analysis.

Test plan

• Verify C5.2.10 numbering does not conflict with existing controls
• Verify cross-references to ASVS 14.1.1, C5.2.4, C5.2.7 are accurate
• Confirm Level 2 assignment is appropriate

Closes #671

[RicoKomenda]

@emmanuelgjr:
After thinking about it, could you do it as a general scope note to the section 5.2 itself? Also you need to renumber because of another merge... :)