fix: prevent white background flash and overscroll on Safari iOS

- Set background-color: #101010 on html/body/.App so the Safari iOS
  rubber-band overscroll area is dark instead of white
- Always render body background style in ViewLoader (not just during
  Suspense fallback) so keyColour param and --background-color-override
  propagate to the body for the overscroll region
- Add viewport-fit=cover, apple-mobile-web-app meta tags for proper
  iOS notch/safe-area handling
- Fix manifest.json background_color from #ffffff to #101010
- Align theme_color across both manifests to #101010

https://claude.ai/code/session_016z5vU45pexTdkQV2eHJqh4

apps/client/public/manifest.json

@@ -14,6 +14,6 @@
   "scope": "./",
   "start_url": "./",
   "display": "",
-  "theme_color": "#121212",
-  "background_color": "#ffffff"
+  "theme_color": "#101010",
+  "background_color": "#101010"
 }

apps/client/public/site.webmanifest

@@ -2,7 +2,7 @@
   "name": "",
   "short_name": "",
   "icons": [{ "src": "ontime-logo.png", "sizes": "295x295", "type": "image/png" }],
-  "theme_color": "#2B5ABC",
+  "theme_color": "#101010",
   "background_color": "#101010",
   "display": "standalone"
 }