feat: Remove enabled checkbox + group payments by provider

1. Remove Enable/Disable Checkbox ✅
   - Already controlled by toggle in main UI
   - Skip rendering 'enabled' field in GenericGatewayForm
   - Cleaner form, less redundancy

2. Use Field Default as Default Value ✅
   - Already working: field.value ?? field.default
   - Backend sends current value, falls back to default
   - No changes needed

3. Group Online Payments by Provider ✅
   - Installed @radix-ui/react-accordion
   - Created accordion.tsx component
   - Group by gateway.title (provider name)
   - Show provider with method count
   - Expand to see individual methods

   Structure:
   TriPay (3 payment methods)
     ├─ BNI Virtual Account
     ├─ Mandiri Virtual Account
     └─ BCA Virtual Account

   PayPal (1 payment method)
     └─ PayPal

Benefits:
- Cleaner UI with less clutter
- Easy to find specific provider
- Shows method count at a glance
- Multiple providers can be expanded
- Better organization for many gateways

Files Modified:
- GenericGatewayForm.tsx: Skip enabled field
- Payments.tsx: Accordion grouping by provider
- accordion.tsx: New component (shadcn pattern)

Next: Dialog/Drawer responsive pattern

admin-spa/src/components/ui/accordion.tsx

@@ -0,0 +1,56 @@
+import * as React from "react"
+import * as AccordionPrimitive from "@radix-ui/react-accordion"
+import { ChevronDown } from "lucide-react"
+
+import { cn } from "@/lib/utils"
+
+const Accordion = AccordionPrimitive.Root
+
+const AccordionItem = React.forwardRef<
+  React.ElementRef<typeof AccordionPrimitive.Item>,
+  React.ComponentPropsWithoutRef<typeof AccordionPrimitive.Item>
+>(({ className, ...props }, ref) => (
+  <AccordionPrimitive.Item
+    ref={ref}
+    className={cn("border-b", className)}
+    {...props}
+  />
+))
+AccordionItem.displayName = "AccordionItem"
+
+const AccordionTrigger = React.forwardRef<
+  React.ElementRef<typeof AccordionPrimitive.Trigger>,
+  React.ComponentPropsWithoutRef<typeof AccordionPrimitive.Trigger>
+>(({ className, children, ...props }, ref) => (
+  <AccordionPrimitive.Header className="flex">
+    <AccordionPrimitive.Trigger
+      ref={ref}
+      className={cn(
+        "flex flex-1 items-center justify-between py-4 font-medium transition-all hover:underline [&[data-state=open]>svg]:rotate-180",
+        className
+      )}
+      {...props}
+    >
+      {children}
+      <ChevronDown className="h-4 w-4 shrink-0 transition-transform duration-200" />
+    </AccordionPrimitive.Trigger>
+  </AccordionPrimitive.Header>
+))
+AccordionTrigger.displayName = AccordionPrimitive.Trigger.displayName
+
+const AccordionContent = React.forwardRef<
+  React.ElementRef<typeof AccordionPrimitive.Content>,
+  React.ComponentPropsWithoutRef<typeof AccordionPrimitive.Content>
+>(({ className, children, ...props }, ref) => (
+  <AccordionPrimitive.Content
+    ref={ref}
+    className="overflow-hidden text-sm transition-all data-[state=closed]:animate-accordion-up data-[state=open]:animate-accordion-down"
+    {...props}
+  >
+    <div className={cn("pb-4 pt-0", className)}>{children}</div>
+  </AccordionPrimitive.Content>
+))
+
+AccordionContent.displayName = AccordionPrimitive.Content.displayName
+
+export { Accordion, AccordionItem, AccordionTrigger, AccordionContent }