Add stage 5: list detail page with items UI and drag reorder

API: new PUT /api/lists/{id}/items/order takes the full ordered id set and
rewrites positions 0..n-1 in a transaction (422 unless the set matches the
list exactly). TodoItemRepository gains idsForList() and reorder().

Frontend: lists on the home page are now links to /lists/:id (ListView).
ListView shows the list title, a "M of N done" summary, and each item as a
drag handle + checkbox + inline-editable text (saved on blur) + delete
button, with a create-item form at the bottom. Drag-and-drop uses
vuedraggable; on drop the whole order is persisted via the new endpoint and
the response replaces local state, with a resync-on-error fallback. New
items store; items store is also reset on logout.

Tests: reorder happy path, incomplete-set rejection, owner scoping. Backend
suite: 23 passing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/types.ts

@@ -23,6 +23,16 @@ export interface TodoList {
   updated_at: string
 }
 
+export interface TodoItem {
+  id: number
+  list_id: number
+  text: string
+  complete: boolean
+  position: number
+  created_at: string
+  updated_at: string
+}
+
 /** Shape of every error body returned by the API. */
 export interface ApiErrorBody {
   error: {