fix: 附件上传改用 UiFile changed + fetch FormData

UiFile changed 事件 → script fetch POST multipart → 成功后 render Tabular
无需点击上传按钮，选择文件即自动上传

wwwroot/api/contract_attach.ui

@@ -23,19 +23,20 @@
             }
         },
         {
-            "widgettype": "Form",
-            "id": "upload_form",
+            "widgettype": "UiFile",
+            "id": "file_input",
             "options": {
-                "submit_url": "{{entire_url('/filemgr/upload_file.dspy')}}",
-                "fields": [
-                    {"name": "folderid", "uitype": "hide", "value": "{{folder}}"},
-                    {"name": "fiid", "uitype": "hide", "value": "{{fiid}}"},
-                    {"name": "upfile", "uitype": "file", "multiple": true, "label": "选择文件"}
-                ],
-                "buttons": [
-                    {"name": "submit", "label": "上传", "css": "primary"}
-                ]
-            }
+                "name": "upfile",
+                "multiple": true,
+                "label": "选择文件（支持多选及拖拽）",
+                "cwidth": 30
+            },
+            "binds": [{
+                "wid": "self",
+                "event": "changed",
+                "actiontype": "script",
+                "script": "var files=this.get_files();if(!files||!files.length)return;var fd=new FormData();fd.append('folderid','{{folder}}');fd.append('fiid','{{fiid}}');for(var i=0;i<files.length;i++)fd.append('upfile',files[i]);var self=this;fetch('{{entire_url(\"/filemgr/upload_file.dspy\")}}',{method:'POST',body:fd}).then(function(r){if(r.ok){var tbl=bricks.app.getWidgetById('attach_tbl');if(tbl)tbl.render({});}else{r.text().then(function(t){bricks.app.show_error('上传失败',t)})}}).catch(function(e){bricks.app.show_error('上传失败',e.message)})"
+            }]
         },
         {
             "widgettype": "Tabular",