Define statistical profile schema and extract profiles from real OHLCV

Parent Feature: #42
Parent roadmap: #28

## Scope
Create a versioned profile describing measurable characteristics of a reference OHLCV dataset.

## Acceptance criteria
- profile fields have precise definitions;
- extraction records source window/timeframe/schema;
- outputs are deterministic for the same input;
- profile contains only statistics the system can actually validate/generate against.