feat(mobile): add AsyncStorage dep + env reader + theme constants

apps/mobile/.env.example

@@ -0,0 +1,7 @@
+# Copy to `.env.local` and fill in. Expo bundles only EXPO_PUBLIC_* vars
+# into the JS, which is what we want for these — they are public Supabase
+# project keys (anon key + URL) protected by RLS on the server.
+
+EXPO_PUBLIC_SUPABASE_URL=https://your-supabase-host.example
+EXPO_PUBLIC_SUPABASE_ANON_KEY=sb_publishable_...
+EXPO_PUBLIC_AUTH_REDIRECT_URL=netralax://auth/callback