Expose ontology editing endpoint

[krapfj23]

Summary

Add GET/PUT endpoints so users can view and manually refine the auto-generated ontology.

Blocked by

• Implement auto-ontology generation #75 (implement auto-ontology generation)

Blocks

Nothing

Steps

1. Add GET /ontology?dataset=<name> — returns the current ontology content (OWL/TTL) for a dataset
2. Add PUT /ontology?dataset=<name> — accepts updated ontology content, validates format (parseable OWL/TTL), saves to file
3. Add Pydantic models for request/response
4. After a manual edit, the next cognify() call for that dataset should use the updated ontology
5. Write tests: GET returns current ontology, PUT updates it, invalid OWL returns 400

Acceptance Criteria

• GET /ontology?dataset=X returns the current ontology
• PUT /ontology?dataset=X updates it and validates format
• Invalid OWL/TTL returns 400
• Next ingestion uses the manually edited ontology
• PR body includes Closes #76