feat: add marketplace metrics, privacy features, and service registry endpoints

- Add Prometheus metrics for marketplace API throughput and error rates with new dashboard panels
- Implement confidential transaction models with encryption support and access control
- Add key management system with registration, rotation, and audit logging
- Create services and registry routers for service discovery and management
- Integrate ZK proof generation for privacy-preserving receipts
- Add metrics instru

enterprise-connectors/python-sdk/aitbc_enterprise/payments/square.py

@@ -0,0 +1,33 @@
+"""
+Square payment connector for AITBC Enterprise (Placeholder)
+"""
+
+from .base import PaymentConnector, PaymentMethod, Charge, Refund, Subscription
+
+
+class SquareConnector(PaymentConnector):
+    """Square payment processor connector"""
+    
+    def __init__(self, client, config, square_access_token):
+        # TODO: Implement Square connector
+        raise NotImplementedError("Square connector not yet implemented")
+    
+    async def create_charge(self, amount, currency, source, description=None, metadata=None):
+        # TODO: Implement Square charge creation
+        raise NotImplementedError
+    
+    async def create_refund(self, charge_id, amount=None, reason=None):
+        # TODO: Implement Square refund
+        raise NotImplementedError
+    
+    async def create_payment_method(self, type, card, metadata=None):
+        # TODO: Implement Square payment method
+        raise NotImplementedError
+    
+    async def create_subscription(self, customer, items, metadata=None):
+        # TODO: Implement Square subscription
+        raise NotImplementedError
+    
+    async def cancel_subscription(self, subscription_id, at_period_end=True):
+        # TODO: Implement Square subscription cancellation
+        raise NotImplementedError