feat: per newsletter folder move setting

frontend/src/app/page.tsx

@@ -73,6 +73,7 @@ export default function LetterFeedApp() {
 
         <AddNewsletterDialog
           isOpen={isAddDialogOpen}
+          folderOptions={folderOptions}
           onOpenChange={setIsAddDialogOpen}
           onSuccess={fetchData}
         />
@@ -81,6 +82,7 @@ export default function LetterFeedApp() {
           <EditNewsletterDialog
             newsletter={editingNewsletter}
             isOpen={isEditDialogOpen}
+            folderOptions={folderOptions}
             onOpenChange={setIsEditDialogOpen}
             onSuccess={() => {
               setEditingNewsletter(null)

frontend/src/lib/api.ts

@@ -10,6 +10,7 @@ export interface Newsletter {
   id: number
   name: string
   is_active: boolean
+  move_to_folder?: string | null
   extract_content: boolean
   senders: { id: number; email: string }[]
   entries_count: number
@@ -18,12 +19,14 @@ export interface Newsletter {
 export interface NewsletterCreate {
     name: string;
     sender_emails: string[];
+    move_to_folder?: string | null;
     extract_content: boolean;
 }
 
 export interface NewsletterUpdate {
     name: string;
     sender_emails: string[];
+    move_to_folder?: string | null;
     extract_content: boolean;
 }