Folders can now contain other folders, to arbitrary depth, via a
self-referencing parent_folder_id (ON DELETE SET NULL, same pattern as
lists.folder_id). Nesting/un-nesting is drag-and-drop only: dropping a
folder onto another folder's header middle moves it in, the outer
quarters or any top-level/in-folder drop insert it beside a target.
Dropping a folder into itself or one of its own subfolders is silently
ignored. Deleting a folder releases its lists and subfolders back to
the top level, unchanged from the existing list behavior.
ListFolderNavItemViewModel.Lists became Children (object, mixing lists
and subfolders, mirroring TopLevel) so the existing implicit, type-matched
DataTemplates render nested folders recursively without new XAML, and each
nesting level gets its indent for free from the folder template's own
margin. Folders/RootLists/ContainerOf/PersistOrderAsync/RecomputeFolderCounts
now walk the tree instead of assuming one level.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Die oberste Sidebar-Ebene ist jetzt eine gemischte TopLevel-Collection, so
dass eine Liste auch oberhalb eines Ordners stehen kann. DropAsync deckt
alle vier Quelle/Ziel-Kombinationen ab, ReorderSidebarAsync numeriert die
gesamte sichtbare Reihenfolge ueber lists und list_folders hinweg.
Data: folder delete keeps its lists (ON DELETE SET NULL), rename patches
name/icon without resetting sort order or collapse state.
Sidebar: grouping on load, folder badge as the sum of its children, both
move routes, and the persisted collapse state.
Drops the LoadAsync/AddRowAsync normalization of a dangling folder_id:
FK enforcement is on for every connection, so the row it guarded against
cannot exist, and ContainerOf already falls back to the top level.
