fix: view_assets — use actiontype:urlwidget + target + mode:replace

Replace custom JS fetch script with proper bricks-native pattern:
- actiontype: urlwidget, target: app.rl_asset_results, mode: replace
- method: POST in urlwidget options (required for form data)
- Remove duplicate id from dspy response widgets (id belongs to container only)

wwwroot/api/submit_list_assets.dspy

@@ -22,7 +22,6 @@ assets = result.get('assets', [])
 if not assets:
     return json.dumps({
         "widgettype": "VBox",
-        "id": "rl_asset_results",
         "options": {"padding": "16px", "gap": "12px"},
         "subwidgets": [
             {
@@ -131,7 +130,6 @@ for a in assets:
 # Wrap cards in ResponsableBox for responsive grid
 result_widget = {
     "widgettype": "VBox",
-    "id": "rl_asset_results",
     "options": {"padding": "16px", "gap": "12px"},
     "subwidgets": [
         {"widgettype": "Text", "options": {"text": f"共 {len(assets)} 个素材", "fontWeight": "bold"}},

wwwroot/view_assets.ui

@@ -35,9 +35,13 @@
                 {
                     "wid": "self",
                     "event": "submit",
-                    "actiontype": "script",
-                    "target": "self",
-                    "script": "(async function(){var form=bricks.getWidgetById('view_assets_form',bricks.app);if(!form)return;var vals=form._getValue();var params=new URLSearchParams();for(var k in vals){if(vals[k]!==undefined&&vals[k]!==null)params.append(k,vals[k])}var url=bricks.app.baseUrl+'/reallife_asset/api/submit_list_assets.dspy?_webbricks_=1';var resp=await fetch(url,{method:'POST',body:params});var desc=await resp.json();var target=bricks.getWidgetById('rl_asset_results',bricks.app);if(!target)return;if(target.destroy_subwidgets)target.destroy_subwidgets();target.subwidgets=[];target.el.innerHTML='';if(desc&&desc.widgettype){await bricks.widgetBuild(desc,target)}})()"
+                    "actiontype": "urlwidget",
+                    "target": "app.rl_asset_results",
+                    "options": {
+                        "method": "POST",
+                        "url": "{{entire_url('api/submit_list_assets.dspy')}}"
+                    },
+                    "mode": "replace"
                 }
             ]
         },