fix(pwa): fix UI overlap, scroll bleed and wrong nav height on iOS

Three root causes fixed:

1. Double safe-area padding: pwa.css set padding-top/bottom on body
   globally, but page containers already account for safe-area-inset
   in their height calculations. Removed body vertical padding (kept
   only in standalone media query for padding-top).

2. Wrong nav token: all page containers used --nav-height-mobile (56px)
   instead of --nav-bottom-height (68px = 56px scroll + 12px dots),
   causing 12px of content to render behind the bottom nav.

3. Scroll bleed: fixed-height page containers lacked overflow:hidden,
   allowing scroll events to propagate to the body. Added
   overscroll-behavior-y:contain on app-content globally.

Fixes #16

package.json

@@ -1,6 +1,6 @@
 {
   "name": "oikos",
-  "version": "0.8.1",
+  "version": "0.8.2",
   "description": "Self-hosted family planner - calendar, tasks, shopping, meal planning, budget and more. Private, open-source, no subscription.",
   "main": "server/index.js",
   "type": "module",