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/(app)/(tabs)/profile/_layout.tsx

@@ -17,8 +17,6 @@ export default function ProfileStackLayout() {
       <Stack.Screen name="blocked-users" />
       <Stack.Screen name="chat-settings" />
       <Stack.Screen name="about" />
-      <Stack.Screen name="terms" />
-      <Stack.Screen name="privacy" />
       <Stack.Screen name="verification" />
       <Stack.Screen name="data-storage" />
       <Stack.Screen name="privacy-settings" />

app/(app)/(tabs)/profile/privacy.tsx

@@ -1,5 +0,0 @@
-import { PrivacyPolicyScreen } from '../../../../src/screens/profile/PrivacyPolicyScreen';
-
-export default function PrivacyPolicyRoute() {
-  return <PrivacyPolicyScreen />;
-}

app/(app)/(tabs)/profile/terms.tsx

@@ -1,5 +0,0 @@
-import { TermsOfServiceScreen } from '../../../../src/screens/profile/TermsOfServiceScreen';
-
-export default function TermsOfServiceRoute() {
-  return <TermsOfServiceScreen />;
-}