fix: 修复知识库目录浏览按钮无响应——为 dialog 插件补充 capabilities 权限，选择器异常改为前端可见

ui/src/pages/KnowledgeBasePage.tsx

@@ -777,9 +777,11 @@ function SourceModal({
   const [path, setPath] = useState("");
   const [extensions, setExtensions] = useState("");
   const [recursive, setRecursive] = useState(true);
+  const [browseMsg, setBrowseMsg] = useState<string | null>(null);
   const valid = path.trim().length > 0;
 
   async function handleBrowse() {
+    setBrowseMsg(null);
     try {
       const dir = await openDialog({
         directory: true,
@@ -788,9 +790,11 @@ function SourceModal({
       });
       if (typeof dir === "string" && dir) {
         setPath(dir);
+      } else {
+        setBrowseMsg("已取消选择");
       }
-    } catch {
-      // 取消或选择器异常时不改变当前输入
+    } catch (e) {
+      setBrowseMsg(`无法打开文件夹选择器：${String(e)}`);
     }
   }
 
@@ -827,6 +831,9 @@ function SourceModal({
                 浏览…
               </button>
             </div>
+            {browseMsg ? (
+              <div className="mt-1 text-[11px] text-slate-500">{browseMsg}</div>
+            ) : null}
           </div>
           <div>
             <label className="mb-1 block text-xs text-slate-400">后缀过滤（可选）</label>