✨ feat(pricing+endpoints+ui): wire custom endpoint mapping end‑to‑end and overhaul visual JSON editor

Backend (Go)
- Include custom endpoints in each model’s SupportedEndpointTypes by parsing Model.Endpoints (JSON) and appending keys alongside native endpoint types.
- Build a global supportedEndpointMap map[string]EndpointInfo{path, method} by:
  - Seeding with native defaults.
  - Overriding/adding from models.endpoints (accepts string path → default POST, or {path, method}).
- Expose supported_endpoint at the top level of /api/pricing (vendors-like), removing per-model duplication.
- Fix default path for EndpointTypeOpenAIResponse to /v1/responses.
- Keep concurrency/caching for pricing retrieval intact.

Frontend (React)
- Fetch supported_endpoint in useModelPricingData and propagate to PricingPage → ModelDetailSideSheet → ModelEndpoints.
- ModelEndpoints
  - Resolve path+method via endpointMap; replace {model} with actual model name.
  - Fix mobile visibility; always show path and HTTP method.
- JSONEditor
  - Wrap with Form.Slot to inherit form layout; simplify visual styles.
  - Use Tabs for “Visual” / “Manual” modes.
  - Unify editors: key-value editor now supports nested JSON:
    - “+” to convert a primitive into an object and add nested fields.
    - Add “Convert to value” for two‑way toggle back from object.
    - Stable key rename without reordering rows; new rows append at bottom.
    - Use Row/Col grid for clean alignment; region editor uses Form.Slot + grid.
- Editing flows
  - EditModelModal / EditPrefillGroupModal use JSONEditor (editorType='object') for endpoint mappings.
  - PrefillGroupManagement renders endpoint group items by JSON keys.

Data expectations / compatibility
- models.endpoints should be a JSON object mapping endpoint type → string path or {path, method}. Strings default to POST.
- No schema changes; existing TEXT field continues to store JSON.

QA
- /api/pricing now returns custom endpoint types and global supported_endpoint.
- UI shows both native and custom endpoints; paths/methods render on mobile; nested editing works and preserves order.

web/src/components/table/models/modals/PrefillGroupManagement.jsx

@@ -137,8 +137,22 @@ const PrefillGroupManagement = ({ visible, onClose }) => {
       title: t('项目内容'),
       dataIndex: 'items',
       key: 'items',
-      render: (items) => {
+      render: (items, record) => {
         try {
+          if (record.type === 'endpoint') {
+            const obj = typeof items === 'string' ? JSON.parse(items || '{}') : (items || {});
+            const keys = Object.keys(obj);
+            if (keys.length === 0) return <Text type="tertiary">{t('暂无项目')}</Text>;
+            return renderLimitedItems({
+              items: keys,
+              renderItem: (key, idx) => (
+                <Tag key={idx} size="small" shape='circle' color={stringToColor(key)}>
+                  {key}
+                </Tag>
+              ),
+              maxDisplay: 3,
+            });
+          }
           const itemsArray = typeof items === 'string' ? JSON.parse(items) : items;
           if (!Array.isArray(itemsArray) || itemsArray.length === 0) {
             return <Text type="tertiary">{t('暂无项目')}</Text>;