fix: correct cookie domain for .local TLD hostnames

getCookieDomain() returns '.localhost' for hostnames ending in '.local'
(e.g., app.plunk.local), causing the browser to reject the cookie
because the domain doesn't match the request origin.

Split the .localhost and .local cases so that .local hostnames return
the actual base domain (e.g., .plunk.local).

apps/api/src/services/UserService.ts

@@ -10,6 +10,7 @@ import {Keys} from './keys.js';
  * Extract base domain from URL for cookie sharing across subdomains
  * e.g., "http://api.example.com" -> ".example.com"
  * e.g., "http://api.localhost" -> ".localhost"
+ * e.g., "http://app.plunk.local" -> ".plunk.local"
  */
 function getCookieDomain(): string | undefined {
   if (NODE_ENV === 'development') {
@@ -28,10 +29,14 @@ function getCookieDomain(): string | undefined {
     // Extract base domain (last two parts for most domains, or .localhost)
     const parts = hostname.split('.');
     if (parts.length >= 2) {
-      // For *.localhost or *.local, use the full hostname with leading dot
-      if (hostname.endsWith('.localhost') || hostname.endsWith('.local')) {
+      // For *.localhost, use .localhost (reserved TLD)
+      if (hostname.endsWith('.localhost')) {
         return '.localhost';
       }
+      // For *.local (mDNS TLD), use the actual base domain
+      if (hostname.endsWith('.local')) {
+        return `.${parts.slice(-2).join('.')}`;
+      }
       // For other domains, use the last two parts (e.g., .example.com)
       return `.${parts.slice(-2).join('.')}`;
     }