Improve speaker invites and redesign roster add flow.

Surface specific send failures, allow resend, use ladl.link portal URLs, and replace stacked speaker forms with a single add-to-list pattern.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/Services/Billing/PlatformEmailClient.php

@@ -19,7 +19,7 @@ class PlatformEmailClient
 
     public function send(string $ownerPublicId, string $to, string $subject, string $html, ?string $text = null): bool
     {
-        if ($this->token() === '') {
+        if (! $this->isConfigured()) {
             return false;
         }
 
@@ -54,4 +54,9 @@ class PlatformEmailClient
             return false;
         }
     }
+
+    public function isConfigured(): bool
+    {
+        return $this->token() !== '';
+    }
 }