feat(dashboard): add shopping list widget

Show shopping lists with open items directly on the dashboard.
Each list displays a progress bar, the first few unchecked items,
and a "+N more" overflow indicator. Widget only appears when there
are lists with open items.

Backend: new shoppingLists query in /api/v1/dashboard (up to 3 lists,
6 open items each). Frontend: renderShoppingLists() widget following
existing widget pattern. CSS: compact list/progress/item styles.
i18n: shoppingMore key added to de/en/it.

Requested in discussion #9

package.json

@@ -1,6 +1,6 @@
 {
   "name": "oikos",
-  "version": "0.7.7",
+  "version": "0.8.0",
   "description": "Self-hosted family planner - calendar, tasks, shopping, meal planning, budget and more. Private, open-source, no subscription.",
   "main": "server/index.js",
   "type": "module",