feat(notebook): lock material source to notebook when studioToken is provided

- Auto-switch materialSource to 'notebook' on mount when initialNotebookId is set
- Replace material source dropdown with static label when studioToken is present

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend-web/src/open-canvas/components/ai-writing/AIWritingForm.tsx

@@ -97,6 +97,14 @@ export function AIWritingForm({
     [models, modelName],
   );
 
+  // initialNotebookId 存在时自动切换素材来源为「我的笔记」
+  useEffect(() => {
+    if (initialNotebookId != null) {
+      setMaterialSource('notebook');
+    }
+  // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
   // 初始化时加载文章类型
   useEffect(() => {
     refreshTypes();
@@ -276,6 +284,12 @@ export function AIWritingForm({
 
         <div className="mt-4 space-y-2">
           <label className={FIELD_LABEL_CLASS}>素材来源</label>
+          {/* studioToken 模式：素材来源已锁定为「我的笔记」，不可切换 */}
+          {studioToken ? (
+            <div className={`${FIELD_TRIGGER_CLASS} flex items-center px-3 border rounded-xl bg-white text-sm text-muted-foreground`}>
+              我的笔记
+            </div>
+          ) : (
             <Select
               value={materialSource}
               onValueChange={(v) => handleMaterialSourceChange(v as MaterialSource)}
@@ -293,6 +307,7 @@ export function AIWritingForm({
                 ))}
               </SelectContent>
             </Select>
+          )}
 
           {/* 选了"我的笔记"才展示笔记本 / 文档选择器 */}
           {materialSource === 'notebook' && (