Opt-in ECO codes for evidence items in validation reports #9

Since 0.6.0 each extraction_method value carries an ECO term in the LinkML schema (meaning:, see docs/STANDARDS.md), but reports do not show them. Add an opt-in way to include the ECO code for every evidence item in a validation report, so downstream systems that speak ECO can use it directly.

Constraints

• Opt-in only. The default report must stay byte-for-byte identical, because committed benchmark results and audit hashes depend on it. Suggested: bioevidence validate --annotate-eco and a matching keyword argument in Python.
• Read the codes from the schema (SchemaView(...).get_enum("ExtractionMethod")), do not hard-code them, so the mapping has one source of truth.

Where to look

• src/bioevidence_validator/engine.py (RecordValidator.validate builds the report), src/bioevidence_validator/cli.py
• tests/test_standards.py shows how to read the meanings

Done when

• With the flag, the report contains, for each evidence item id, its extraction method and ECO CURIE
• Without the flag, reports are unchanged (the existing replay tests still pass)
• Tests for both, and a short note in docs/STANDARDS.md and docs/ENGINEERING.md