feat: add authenticated identity resolution API endpoints

[uguracikgoz]

• Created identity_resolution_endpoint.py with 7 endpoints for profile merging operations
• All endpoints require authentication and admin/developer roles
• Integrated with IdentityResolutionService from tracardi core
• Added endpoints: validate-profile, merge-by-ids, merge-by-keys, merge-by-field, find-duplicates, detect-circular-merge, check-resurrection
• Registered router in app/main.py
• Includes comprehensive docstrings and error handling

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