fix(shifts): expose ExternalUserId in ShiftSignupDto to fix frontend signup state

backend/WorkClub.Api/Services/MemberSyncService.cs

@@ -41,6 +41,20 @@ public class MemberSyncService
         }
 
         var email = httpContext.User.FindFirst("email")?.Value ?? httpContext.User.FindFirst("preferred_username")?.Value ?? "unknown@example.com";
+
+        // If not found by ExternalUserId, try to find by Email (for seeded users)
+        var memberByEmail = await _context.Members
+            .FirstOrDefaultAsync(m => m.Email == email && m.TenantId == tenantId);
+            
+        if (memberByEmail != null)
+        {
+            // Update the seeded user with the real ExternalUserId
+            memberByEmail.ExternalUserId = externalUserId;
+            memberByEmail.UpdatedAt = DateTimeOffset.UtcNow;
+            await _context.SaveChangesAsync();
+            return;
+        }
+
         var name = httpContext.User.FindFirst("name")?.Value ?? email.Split('@')[0];
 
         var roleClaim = httpContext.User.FindFirst(System.Security.Claims.ClaimTypes.Role)?.Value ?? "Member";