fix(i18n): localize error pages thrown before SetLocale middleware

CSRF (419), unmatched-route 404 and maintenance (503) errors are thrown before
the web-group SetLocale middleware runs, so the custom error pages rendered in
the default locale for EN users. Extract SetLocale::apply() (session-guarded, so
it is safe pre-session) and call it from a withExceptions render hook that falls
through to the normal renderer — the error views now honour the user's language
where it is known.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/Http/Middleware/SetLocale.php

@@ -18,14 +18,30 @@ class SetLocale
 
     public function handle(Request $request, Closure $next): Response
     {
+        self::apply($request);
+
+        return $next($request);
+    }
+
+    /**
+     * Resolve + set the active locale: signed-in user's preference, then the session
+     * choice, then the app default. Safe to call before the session is started — e.g.
+     * from the exception handler for errors thrown before this middleware (CSRF 419,
+     * unmatched-route 404, maintenance 503) — a missing session is simply skipped, so
+     * those custom error pages still honour the user's language where it is known.
+     */
+    public static function apply(Request $request): void
+    {
+        $locale = config('app.locale');
+
+        if ($request->hasSession()) {
             $locale = $request->user()?->locale
                 ?? $request->session()->get('locale')
-            ?? config('app.locale');
+                ?? $locale;
+        }
 
         if (in_array($locale, self::SUPPORTED, true)) {
             app()->setLocale($locale);
         }
-
-        return $next($request);
     }
 }

bootstrap/app.php

@@ -42,4 +42,15 @@ return Application::configure(basePath: dirname(__DIR__))
         $exceptions->shouldRenderJsonWhen(
             fn (Request $request) => $request->is('api/*'),
         );
+
+        // Errors thrown BEFORE the web-group SetLocale middleware (CSRF 419, an
+        // unmatched-route 404, maintenance 503) would render the custom error page in
+        // the default locale. Resolve the user's language first so those pages honour
+        // it too (R16); returning null falls through to the normal renderer (the
+        // resources/views/errors/* views).
+        $exceptions->render(function (Throwable $e, Request $request) {
+            SetLocale::apply($request);
+
+            return null;
+        });
     })->create();