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

frontend/src/components/payment/PaymentProviderDialog.vue

@@ -32,7 +32,8 @@
       <!-- Toggles + Payment mode + Supported types (single row) -->
       <div class="flex flex-wrap items-center gap-x-5 gap-y-2">
         <ToggleSwitch :label="t('common.enabled')" :checked="form.enabled" @toggle="form.enabled = !form.enabled" />
-        <ToggleSwitch :label="t('admin.settings.payment.refundEnabled')" :checked="form.refund_enabled" @toggle="form.refund_enabled = !form.refund_enabled" />
+        <ToggleSwitch :label="t('admin.settings.payment.refundEnabled')" :checked="form.refund_enabled" @toggle="form.refund_enabled = !form.refund_enabled; if (!form.refund_enabled) form.allow_user_refund = false" />
+        <ToggleSwitch v-if="form.refund_enabled" :label="t('admin.settings.payment.allowUserRefund')" :checked="form.allow_user_refund" @toggle="form.allow_user_refund = !form.allow_user_refund" />
         <div v-if="form.provider_key === 'easypay'" class="flex items-center gap-2">
           <span class="text-xs font-medium text-gray-500 dark:text-gray-400">{{ t('admin.settings.payment.paymentMode') }}</span>
           <div class="flex gap-1.5">
@@ -243,6 +244,7 @@ const emit = defineEmits<{
     enabled: boolean
     payment_mode: string
     refund_enabled: boolean
+    allow_user_refund: boolean
     config: Record<string, string>
     limits: string
   }]
@@ -258,6 +260,7 @@ const form = reactive({
   enabled: true,
   payment_mode: PAYMENT_MODE_QRCODE,
   refund_enabled: false,
+  allow_user_refund: false,
 })
 const config = reactive<Record<string, string>>({})
 const limits = reactive<Record<string, Record<string, number>>>({})
@@ -433,6 +436,7 @@ function handleSave() {
     enabled: form.enabled,
     payment_mode: form.provider_key === 'easypay' ? form.payment_mode : '',
     refund_enabled: form.refund_enabled,
+    allow_user_refund: form.refund_enabled ? form.allow_user_refund : false,
     config: filteredConfig,
     limits: serializeLimits(),
   })
@@ -452,6 +456,7 @@ function reset(defaultKey: string) {
   form.enabled = true
   form.payment_mode = defaultKey === 'easypay' ? PAYMENT_MODE_QRCODE : ''
   form.refund_enabled = false
+  form.allow_user_refund = false
   clearConfig()
   applyDefaults()
 }
@@ -463,6 +468,7 @@ function loadProvider(provider: ProviderInstance) {
   form.enabled = provider.enabled
   form.payment_mode = provider.payment_mode || (provider.provider_key === 'easypay' ? PAYMENT_MODE_QRCODE : '')
   form.refund_enabled = provider.refund_enabled
+  form.allow_user_refund = provider.allow_user_refund
   clearConfig()
   // Pre-fill config from API response (non-sensitive in cleartext, sensitive masked as ••••••••)
   if (provider.config) {