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();
@@ -276,23 +284,30 @@ export function AIWritingForm({
 
         <div className="mt-4 space-y-2">
           <label className={FIELD_LABEL_CLASS}>素材来源</label>
-          <Select
-            value={materialSource}
-            onValueChange={(v) => handleMaterialSourceChange(v as MaterialSource)}
-            disabled={disabled}
-          >
-            <SelectTrigger className={FIELD_TRIGGER_CLASS}>
-              <SelectValue placeholder="选择素材来源" />
-            </SelectTrigger>
-            <SelectContent>
-              {MATERIAL_SOURCE_OPTIONS.map((opt) => (
-                <SelectItem key={opt.value} value={opt.value} className="text-sm">
-                  {opt.label}
-                  <span className="ml-1 text-xs text-muted-foreground">— {opt.desc}</span>
-                </SelectItem>
-              ))}
-            </SelectContent>
-          </Select>
+          {/* 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)}
+              disabled={disabled}
+            >
+              <SelectTrigger className={FIELD_TRIGGER_CLASS}>
+                <SelectValue placeholder="选择素材来源" />
+              </SelectTrigger>
+              <SelectContent>
+                {MATERIAL_SOURCE_OPTIONS.map((opt) => (
+                  <SelectItem key={opt.value} value={opt.value} className="text-sm">
+                    {opt.label}
+                    <span className="ml-1 text-xs text-muted-foreground">— {opt.desc}</span>
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          )}
 
           {/* 选了"我的笔记"才展示笔记本 / 文档选择器 */}
           {materialSource === 'notebook' && (