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/src/views/ViewLoader.tsx

@@ -23,15 +23,19 @@ export default function ViewLoader({ children }: PropsWithChildren) {
   const searchParams = new URLSearchParams(window.location.search);
   const colourFromParams = searchParams.get('keyColour') ?? '#101010';
 
+  // always keep body background in sync so Safari iOS overscroll area matches the view
+  const bodyBgStyle = `body { background-color: var(--background-color-override, ${colourFromParams}); }`;
+
   return (
     <Suspense
       fallback={
         <>
-          <style>{`body { background: var(--background-color-override, ${colourFromParams}); }`}</style>
+          <style>{bodyBgStyle}</style>
           <Loader />
         </>
       }
     >
+      <style>{bodyBgStyle}</style>
       <OverrideStyles />
       {children}
     </Suspense>