[Feature] Subjective feedback ontology and versioning

[shchukins]

Parent

Part of #82.

Idea

Document and version subjective feedback types, scales, and mappings.

Problem

Subjective feedback will evolve. Without versioning, historical datasets become ambiguous.

Proposed solution

Create documentation and constants for:

• feedback_type
• feedback_value
• feedback_score
• source mappings
• sport-specific extensions
• deprecated values
• versioning rules

Requirements

• no uncontrolled string proliferation
• every feedback type has clear semantics
• every score scale has documented direction
• source mappings are reproducible

Acceptance criteria

• docs explain all active feedback types
• backend uses centralized constants/mapping where practical
• dataset export can identify feedback schema version