Add branded boot splash (Ladill Mail style) on app pages

InjectBootSplash middleware shows a self-branded loading splash once per session
while the app boots, then fades out.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bootstrap/app.php

@@ -24,6 +24,7 @@ return Application::configure(basePath: dirname(__DIR__))
             'platform.session' => \App\Http\Middleware\EnsurePlatformSession::class,
         ]);
         $middleware->web(append: [
+            \App\Http\Middleware\InjectBootSplash::class,
             \App\Http\Middleware\SetActingAccount::class,
         ]);
     })