Phase 3.4: customers.display_name nullable + identity-only social scope

Drop NOT NULL on customers.display_name so phone-OTP and social signups can
land before the user picks a name; frontend then routes them to /auth/set-name.
Google sign-in no longer requests the name claim and Apple SDK scope is
trimmed to email only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/services/auth.service.js

@@ -112,16 +112,18 @@ export const signInWithGoogle = async ({ idToken, anonymousCustomerId, deviceInf
   if (existing) {
     customer = existing
   } else if (anonymousCustomerId) {
+    // Preserve the anonymous display_name; we don't pull name from Google.
     customer = await upgradeCustomerIdentity(anonymousCustomerId, {
       google_sub: google.sub,
       email: google.email,
-      display_name: google.name,
     })
   } else {
+    // No anonymous bootstrap → display_name is null; frontend routes to
+    // the set-display-name screen.
     customer = await createCustomerWithIdentity({
       google_sub: google.sub,
       email: google.email,
-      display_name: google.name,
+      display_name: null,
     })
   }