BREAKING CHANGES:
- vTiger sync: Never overwrites existing vtiger_id
- Contact sync: REPLACES links instead of appending (idempotent)
- E-conomic sync: Only updates fields it owns (address, city, postal, email_domain, website)
- E-conomic sync: Does NOT overwrite name or cvr_number anymore
ARCHITECTURE:
- Each data source owns specific fields
- Sync operations are now idempotent (can run multiple times)
- Clear documentation of field ownership in sync_router.py
- Contact links deleted and recreated on sync to match vTiger state
FIXED:
- Contact relationships now correct after re-sync
- No more mixed customer data from different sources
- Sorting contacts by company_count DESC (companies first)
