feat: Add support for more WooCommerce field types + prepare for sorting

1. Added Support for More Field Types ✅

   New field types:
   - 'title': Heading/separator (renders as h3 with border)
   - 'multiselect': Multiple select dropdown
   - 'account': Bank account repeater (BACS)

   Total supported: text, password, checkbox, select, textarea,
                    number, email, url, account, title, multiselect

2. Improved Account Field Handling ✅

   Problem: WooCommerce might return serialized PHP or JSON string
   Solution: Parse string values before rendering

   Handles:
   - JSON string: JSON.parse()
   - Array: Use directly
   - Empty/invalid: Default to []

   This ensures bank accounts display correctly even if
   backend returns different formats.

3. Added Title Field Support ✅

   Renders as section heading:
   ┌─────────────────────────────┐
   │ Account Details             │ ← Title
   │ Configure your bank...      │ ← Description
   ├─────────────────────────────┤
   │ [Account fields below]      │
   └─────────────────────────────┘

4. Installed DnD Kit for Sorting ✅

   Packages installed:
   - @dnd-kit/core
   - @dnd-kit/sortable
   - @dnd-kit/utilities

   Prepared components:
   - SortableGatewayItem wrapper
   - Drag handle with GripVertical icon
   - DnD sensors and context

   Next: Wire up sorting logic and save order

Why This Matters:
✅ Bank account repeater will now work for BACS
✅ Supports all common WooCommerce field types
✅ Handles different data formats from backend
✅ Better organized settings with title separators
✅ Ready for drag-and-drop sorting

Files Modified:
- GenericGatewayForm.tsx: New field types + parsing
- Payments.tsx: DnD imports + sortable component
- package.json: DnD kit dependencies

admin-spa/package.json

@@ -10,6 +10,9 @@
         "lint": "ESLINT_USE_FLAT_CONFIG=false eslint . --ext ts,tsx --report-unused-disable-directives"
     },
     "dependencies": {
+        "@dnd-kit/core": "^6.3.1",
+        "@dnd-kit/sortable": "^10.0.0",
+        "@dnd-kit/utilities": "^3.2.2",
         "@radix-ui/react-accordion": "^1.2.12",
         "@radix-ui/react-alert-dialog": "^1.1.15",
         "@radix-ui/react-avatar": "^1.1.10",