feat(mail): make notification failures non-fatal

Add App\Support\SafeNotifier that wraps $notifiable->notify() in a
Throwable guard with a logged warning, so SMTP outages (the current
Gmail 535 errors) no longer propagate as a 500 to the user. Apply to
the two hot paths that were still unprotected: CommentController
(new comment, reply, like) and RegisteredUserController (super-admin
registration alert). User::sendEmailVerificationNotification() is
wrapped inline for the same reason.

Also add docs/mail-setup.md covering the three delivery options:
Gmail app password (quick), Mailgun, Postmark — with the exact .env
keys for each.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

app/Models/User.php

@@ -281,7 +281,19 @@ class User extends Authenticatable implements MustVerifyEmail
 
     public function sendEmailVerificationNotification(): void
     {
-        $this->notify(new VerifyEmail);
+        // Mail failures must never bubble up as a 500 to the user — the account
+        // exists, the HTTP request was fine, only the delivery pipe is broken.
+        // We log the failure (ops picks it up) and move on. Re-sending via
+        // `php artisan app:resend-verification` fixes the user once SMTP recovers.
+        try {
+            $this->notify(new VerifyEmail);
+        } catch (\Throwable $e) {
+            \Illuminate\Support\Facades\Log::warning('verify-email send failed', [
+                'user_id' => $this->id,
+                'email'   => $this->email,
+                'error'   => $e->getMessage(),
+            ]);
+        }
     }
 
     // Role helper methods