♻️ refactor(model): replace gorm.io/datatypes with JSONValue for PrefillGroup.Items; fix JSON scan across drivers

- Why:
  - Avoid introducing `gorm.io/datatypes` for a single field.
  - Align with existing pattern (`ChannelInfo`, `Properties`) using `Scanner`/`Valuer`.
  - Fix runtime error when drivers return JSON as string.

- What:
  - Introduced `JSONValue` (based on `json.RawMessage`) implementing `sql.Scanner` and `driver.Valuer`, with `MarshalJSON`/`UnmarshalJSON` to preserve raw JSON in API.
  - Updated `PrefillGroup.Items` to use `JSONValue` with `gorm:"type:json"`.
  - Localized comments in `model/prefill_group.go` to Chinese.

- Impact:
  - Resolves “unsupported Scan, storing driver.Value type string into type *json.RawMessage”.
  - Works with MySQL/Postgres/SQLite whether JSON is returned as `[]byte` or `string`.
  - API and DB schema remain unchanged; no `go.mod` changes; lints pass.

Files changed:
- model/prefill_group.go

web/src/components/table/channels/modals/EditChannelModal.jsx

@@ -1247,11 +1247,7 @@ const EditChannelModal = (props) => {
                       templateLabel={t('填入模板')}
                       editorType="region"
                       formApi={formApiRef.current}
-                      extraText={
-                        <Text type="tertiary" size="small">
-                          {t('设置默认地区和特定模型的专用地区')}
-                        </Text>
-                      }
+                      extraText={t('设置默认地区和特定模型的专用地区')}
                     />
                   )}
 
@@ -1520,11 +1516,7 @@ const EditChannelModal = (props) => {
                     templateLabel={t('填入模板')}
                     editorType="keyValue"
                     formApi={formApiRef.current}
-                    extraText={
-                      <Text type="tertiary" size="small">
-                        {t('键为请求中的模型名称，值为要替换的模型名称')}
-                      </Text>
-                    }
+                    extraText={t('键为请求中的模型名称，值为要替换的模型名称')}
                   />
                 </Card>
 
@@ -1628,11 +1620,7 @@ const EditChannelModal = (props) => {
                     templateLabel={t('填入模板')}
                     editorType="keyValue"
                     formApi={formApiRef.current}
-                    extraText={
-                      <Text type="tertiary" size="small">
-                        {t('键为原状态码，值为要复写的状态码，仅影响本地判断')}
-                      </Text>
-                    }
+                    extraText={t('键为原状态码，值为要复写的状态码，仅影响本地判断')}
                   />
                 </Card>