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

apps/mobile/lib/env.ts

@@ -0,0 +1,19 @@
+// EXPO_PUBLIC_* vars are inlined at bundle time by Expo's Babel plugin.
+// We pull them through a single typed module so a missing var is a loud
+// startup error rather than a confusing Supabase 401 later.
+
+function required(name: string): string {
+  const v = process.env[name];
+  if (!v || v.length === 0) {
+    throw new Error(
+      'Missing required env var ' + name + '. Set it in apps/mobile/.env.local — see .env.example.',
+    );
+  }
+  return v;
+}
+
+export const env = {
+  supabaseUrl: required('EXPO_PUBLIC_SUPABASE_URL'),
+  supabaseAnonKey: required('EXPO_PUBLIC_SUPABASE_ANON_KEY'),
+  authRedirectUrl: process.env.EXPO_PUBLIC_AUTH_REDIRECT_URL ?? 'netralax://auth/callback',
+} as const;