fix(auth): oidc service updates

services/oidcService.js

@@ -707,11 +707,12 @@ async function findOrProvisionUser(claims, config) {
     throw Object.assign(new Error('This account is inactive.'), { status: 403 });
   }
 
-  // Refresh login timestamp and display name from provider claims
+  // Refresh login timestamp; only seed display_name from provider on first login
+  // (display_name IS NULL). Once the user has set one manually, preserve it.
   db.prepare(`
     UPDATE users
     SET last_login_at = datetime('now'),
-        display_name  = COALESCE(?, display_name),
+        display_name  = CASE WHEN display_name IS NULL THEN ? ELSE display_name END,
         updated_at    = datetime('now')
     WHERE id = ?
   `).run(claims.name || null, user.id);