Simplified user info update APIs, DB and frontend to remove separate update functions for each property. Automatically choose preferred username for users as they register, based on display name.

frontend/src/assets/style.css

@@ -817,7 +817,7 @@ th {
   display: grid;
   border-radius: var(--radius-md);
   background: var(--color-surface);
-  padding: 1.1rem 1.25rem;
+  padding: 1rem;
 }
 
 .user-details {