feat: add per-provider allow_user_refund control and align wildcard matching

allow_user_refund:
- Add allow_user_refund field to PaymentProviderInstance ent schema
- Migration 103: ALTER TABLE payment_provider_instances ADD COLUMN
- Cascade logic: disabling refund_enabled auto-disables allow_user_refund
- User refund validation: check provider instance allows user refund
- Admin refund validation: check provider instance allows admin refund
- Subscription refund: deduct days on refund, rollback on failure
- New endpoint: GET /payment/orders/refund-eligible-providers
- Frontend: ToggleSwitch in ProviderCard/Dialog, cascade in SettingsView

Wildcard matching:
- Change findPricingForModel from "longest prefix wins" to "config order
  priority (first match wins)", aligning with channel service behavior

backend/ent/paymentproviderinstance_update.go

@@ -161,6 +161,20 @@ func (_u *PaymentProviderInstanceUpdate) SetNillableRefundEnabled(v *bool) *Paym
 	return _u
 }
 
+// SetAllowUserRefund sets the "allow_user_refund" field.
+func (_u *PaymentProviderInstanceUpdate) SetAllowUserRefund(v bool) *PaymentProviderInstanceUpdate {
+	_u.mutation.SetAllowUserRefund(v)
+	return _u
+}
+
+// SetNillableAllowUserRefund sets the "allow_user_refund" field if the given value is not nil.
+func (_u *PaymentProviderInstanceUpdate) SetNillableAllowUserRefund(v *bool) *PaymentProviderInstanceUpdate {
+	if v != nil {
+		_u.SetAllowUserRefund(*v)
+	}
+	return _u
+}
+
 // SetUpdatedAt sets the "updated_at" field.
 func (_u *PaymentProviderInstanceUpdate) SetUpdatedAt(v time.Time) *PaymentProviderInstanceUpdate {
 	_u.mutation.SetUpdatedAt(v)
@@ -275,6 +289,9 @@ func (_u *PaymentProviderInstanceUpdate) sqlSave(ctx context.Context) (_node int
 	if value, ok := _u.mutation.RefundEnabled(); ok {
 		_spec.SetField(paymentproviderinstance.FieldRefundEnabled, field.TypeBool, value)
 	}
+	if value, ok := _u.mutation.AllowUserRefund(); ok {
+		_spec.SetField(paymentproviderinstance.FieldAllowUserRefund, field.TypeBool, value)
+	}
 	if value, ok := _u.mutation.UpdatedAt(); ok {
 		_spec.SetField(paymentproviderinstance.FieldUpdatedAt, field.TypeTime, value)
 	}
@@ -431,6 +448,20 @@ func (_u *PaymentProviderInstanceUpdateOne) SetNillableRefundEnabled(v *bool) *P
 	return _u
 }
 
+// SetAllowUserRefund sets the "allow_user_refund" field.
+func (_u *PaymentProviderInstanceUpdateOne) SetAllowUserRefund(v bool) *PaymentProviderInstanceUpdateOne {
+	_u.mutation.SetAllowUserRefund(v)
+	return _u
+}
+
+// SetNillableAllowUserRefund sets the "allow_user_refund" field if the given value is not nil.
+func (_u *PaymentProviderInstanceUpdateOne) SetNillableAllowUserRefund(v *bool) *PaymentProviderInstanceUpdateOne {
+	if v != nil {
+		_u.SetAllowUserRefund(*v)
+	}
+	return _u
+}
+
 // SetUpdatedAt sets the "updated_at" field.
 func (_u *PaymentProviderInstanceUpdateOne) SetUpdatedAt(v time.Time) *PaymentProviderInstanceUpdateOne {
 	_u.mutation.SetUpdatedAt(v)
@@ -575,6 +606,9 @@ func (_u *PaymentProviderInstanceUpdateOne) sqlSave(ctx context.Context) (_node
 	if value, ok := _u.mutation.RefundEnabled(); ok {
 		_spec.SetField(paymentproviderinstance.FieldRefundEnabled, field.TypeBool, value)
 	}
+	if value, ok := _u.mutation.AllowUserRefund(); ok {
+		_spec.SetField(paymentproviderinstance.FieldAllowUserRefund, field.TypeBool, value)
+	}
 	if value, ok := _u.mutation.UpdatedAt(); ok {
 		_spec.SetField(paymentproviderinstance.FieldUpdatedAt, field.TypeTime, value)
 	}