Milestone 2: Auto-create ownership_cost when insurance/registration
document is created with cost data (premium or cost field).
- Add OwnershipCostsService integration
- Auto-create cost on document create when amount > 0
- Sync cost changes on document update
- mapDocumentTypeToCostType() validation
- extractCostAmount() for premium/cost field extraction
- CASCADE delete handled by FK constraint
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
