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/where.go

@@ -99,6 +99,11 @@ func RefundEnabled(v bool) predicate.PaymentProviderInstance {
 	return predicate.PaymentProviderInstance(sql.FieldEQ(FieldRefundEnabled, v))
 }
 
+// AllowUserRefund applies equality check predicate on the "allow_user_refund" field. It's identical to AllowUserRefundEQ.
+func AllowUserRefund(v bool) predicate.PaymentProviderInstance {
+	return predicate.PaymentProviderInstance(sql.FieldEQ(FieldAllowUserRefund, v))
+}
+
 // CreatedAt applies equality check predicate on the "created_at" field. It's identical to CreatedAtEQ.
 func CreatedAt(v time.Time) predicate.PaymentProviderInstance {
 	return predicate.PaymentProviderInstance(sql.FieldEQ(FieldCreatedAt, v))
@@ -559,6 +564,16 @@ func RefundEnabledNEQ(v bool) predicate.PaymentProviderInstance {
 	return predicate.PaymentProviderInstance(sql.FieldNEQ(FieldRefundEnabled, v))
 }
 
+// AllowUserRefundEQ applies the EQ predicate on the "allow_user_refund" field.
+func AllowUserRefundEQ(v bool) predicate.PaymentProviderInstance {
+	return predicate.PaymentProviderInstance(sql.FieldEQ(FieldAllowUserRefund, v))
+}
+
+// AllowUserRefundNEQ applies the NEQ predicate on the "allow_user_refund" field.
+func AllowUserRefundNEQ(v bool) predicate.PaymentProviderInstance {
+	return predicate.PaymentProviderInstance(sql.FieldNEQ(FieldAllowUserRefund, v))
+}
+
 // CreatedAtEQ applies the EQ predicate on the "created_at" field.
 func CreatedAtEQ(v time.Time) predicate.PaymentProviderInstance {
 	return predicate.PaymentProviderInstance(sql.FieldEQ(FieldCreatedAt, v))