fix: iOS PWA bottom nav shifting up in standalone mode

In iOS WebKit standalone (home screen) mode, position:fixed elements
move with the page when the body itself becomes scrollable - unlike
regular Safari where fixed elements stay pinned. The root cause was
body having min-height: 100dvh without overflow: hidden, which allowed
body scroll to occur when content overflowed.

Fix: html and body are now overflow: hidden with fixed height (100% / 100dvh)
so all scrolling is confined to .app-content. Service worker bumped to
shell-v30 to force re-download of reset.css on installed PWAs.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "oikos",
-  "version": "0.17.3",
+  "version": "0.17.4",
   "description": "Self-hosted family planner - calendar, tasks, shopping, meal planning, budget and more. Private, open-source, no subscription.",
   "main": "server/index.js",
   "type": "module",