Legacy ALL-CAPS → Markdown migration for MLflow-registered instruction versions

[hiydavid]

Part of epic #173 (Full Unification of GSL Instruction Schema).

Goal

Existing MLflow-registered instruction versions (register_instruction_version in packages/.../optimization/evaluation.py L2222+) are stored in the legacy ALL-CAPS plain-text format (e.g. PURPOSE:\n- ...). After the format change, replaying or loading a legacy version must still work.

Acceptance criteria

• instruction_schema.normalize_instructions(raw) detects legacy ALL-CAPS on input and normalizes to Markdown ## PURPOSE on output
• GSO's _sanitize_plaintext_instructions (optimization/optimizer.py L5137) delegates to normalize_instructions
• Smoke test: load 3–5 existing MLflow-registered instruction versions from a representative workspace, feed through normalizer, assert round-trip stability
• New writes go out in Markdown form only

Dependencies

• Blocked by: shared instruction_schema.py module