feat: show notebook tree hierarchy in note move, tabs, and agent config

- note-card.tsx: parent/child notebook dropdown with indentation
- notes-tabs-view.tsx: tree-structured notebook picker with check marks
- agent-detail-view.tsx: source/target notebook selects with optgroup tree
- Add notebook-tree-select.tsx shared utility component

memento-note/components/notes-tabs-view.tsx

@@ -547,23 +547,36 @@ function NoteMetaSidebar({
                   : <span className="h-3 w-3 shrink-0" />}
                 {t('notes.generalNotes')}
               </button>
-              {notebooks.map((nb) => (
-                <button
-                  key={nb.id}
-                  type="button"
-                  onClick={() => handleMoveToNotebook(nb.id)}
-                  className={cn(
-                    'flex w-full items-center gap-2 rounded px-2 py-1.5 text-[12px] font-medium hover:bg-muted transition-colors',
-                    note.notebookId === nb.id ? 'text-primary' : 'text-foreground/70'
-                  )}
-                >
-                  {note.notebookId === nb.id
-                    ? <Check className="h-3 w-3 shrink-0" />
-                    : <span className="h-3 w-3 shrink-0" />}
-                  {nb.name}
-                </button>
-              ))}
-            </PopoverContent>
+              {notebooks.filter(nb => !nb.parentId).map((nb) => (
+                 <div key={nb.id}>
+                   <button
+                     type="button"
+                     onClick={() => handleMoveToNotebook(nb.id)}
+                     className={cn(
+                       'flex w-full items-center gap-2 rounded px-2 py-1.5 text-[12px] font-medium hover:bg-muted transition-colors',
+                       note.notebookId === nb.id ? 'text-primary' : 'text-foreground/70'
+                     )}
+                   >
+                     {note.notebookId === nb.id ? <Check className="h-3 w-3 shrink-0" /> : <span className="h-3 w-3 shrink-0" />}
+                     {nb.name}
+                   </button>
+                   {notebooks.filter(c => c.parentId === nb.id).map(child => (
+                     <button
+                       key={child.id}
+                       type="button"
+                       onClick={() => handleMoveToNotebook(child.id)}
+                       className={cn(
+                         'flex w-full items-center gap-2 rounded pl-6 pr-2 py-1.5 text-[12px] font-medium hover:bg-muted transition-colors',
+                         note.notebookId === child.id ? 'text-primary' : 'text-foreground/70'
+                       )}
+                     >
+                       {note.notebookId === child.id ? <Check className="h-3 w-3 shrink-0" /> : <span className="h-3 w-3 shrink-0" />}
+                       └ {child.name}
+                     </button>
+                   ))}
+                 </div>
+               ))}
+             </PopoverContent>
           </Popover>
 
           {/* Pin / Unpin */}