fix: eliminate black gap below bottom nav in iOS PWA standalone mode

iOS reserves the home indicator area outside the CSS viewport, leaving
a black strip below the bottom navigation. A fixed body::after pseudo-
element now fills this zone with the surface color. Also added explicit
background-color on body for consistent rendering.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "oikos",
-  "version": "0.19.4",
+  "version": "0.19.5",
   "description": "Self-hosted family planner - calendar, tasks, shopping, meal planning, budget and more. Private, open-source, no subscription.",
   "main": "server/index.js",
   "type": "module",