refactor(navigation): consolidate navigation with href helpers and extract push device hook

- Migrate all navigation calls from magic strings to centralized href helpers
- Extract inline device registration logic into useRegisterPushDevice hook
- Remove unused terms and privacy policy routes from profile stack
- Add hrefTradeDetail helper for trade detail navigation
- Restore routePayloadCache.stashSystemMessage for group request/invite handling
- Change desktop shell tab navigation from replace to push

app/index.tsx

@@ -1,11 +1,12 @@
 import { Redirect } from 'expo-router';
 
 import { useAuthStore } from '../src/stores';
+import { hrefAuthWelcome, hrefHome } from '../src/navigation/hrefs';
 
 export default function Index() {
   const isAuthenticated = useAuthStore((s) => s.isAuthenticated);
   if (isAuthenticated) {
-    return <Redirect href="/home" />;
+    return <Redirect href={hrefHome()} />;
   }
-  return <Redirect href="/welcome" />;
+  return <Redirect href={hrefAuthWelcome()} />;
 }