feat(extraction): extraction job sets domain and management API

[aredenba-rh]

Summary

Add extraction job set configuration storage on knowledge graphs and management APIs for CRUD/validation, modeled after k-extract extraction_jobs.yaml.

Scope

• Domain value objects for job sets (by_instances, by_files)
• Persist config on knowledge graph (JSONB)
• GET/PUT /management/knowledge-graphs/{kg_id}/extraction-jobs
• Entity type options with live instance counts from design artifacts
• Unit tests

Acceptance

• Job sets can be saved/loaded per KG
• Validation matches k-extract rules (description required for by_instances)
• Save triggers job regeneration hook (see feat(ui): add KG manage workspace, data sources maintenance, and extraction chat #749)

Parent: Extraction Jobs UI parity (k-extract phase3)

[aredenba-rh]

Completed in PR #772