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>

app/Http/Middleware/InjectBootSplash.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace App\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Auth;
+use Illuminate\Support\Facades\View;
+use Symfony\Component\HttpFoundation\Response;
+
+/**
+ * Injects a branded boot splash (Ladill Mail style) into authenticated HTML
+ * pages. The splash shows once per browser session while the app loads, then
+ * fades out — masking the client-side boot so the app feels instant.
+ */
+class InjectBootSplash
+{
+    public function handle(Request $request, Closure $next): Response
+    {
+        $response = $next($request);
+
+        if (! $request->isMethod('GET') || ! Auth::check()) {
+            return $response;
+        }
+
+        if (! str_contains((string) $response->headers->get('Content-Type', ''), 'text/html')) {
+            return $response;
+        }
+
+        $content = $response->getContent();
+        if (! is_string($content)
+            || stripos($content, '<body') === false
+            || str_contains($content, 'id="ladill-boot"')) {
+            return $response;
+        }
+
+        $splash = View::make('partials.boot-splash')->render();
+        $content = preg_replace_callback('/<body\b[^>]*>/i', fn ($m) => $m[0].$splash, $content, 1);
+
+        if (is_string($content)) {
+            $response->setContent($content);
+        }
+
+        return $response;
+    }
+}