fix: redirects 301 not firing — three bugs

- toPages()->first() instead of toPage() (pages field stores YAML array)
- Force read from default language content to avoid empty rules on FR requests
- Add error.php template so Kirby uses the error controller (without it,
  Kirby fell back to default template and ignored site/controllers/error.php)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

site/controllers/error.php

@@ -13,11 +13,13 @@ return function ($kirby, $page, $site) {
             $map = [];
             $redirectsPage = $site->find('redirections');
             if ($redirectsPage) {
-                foreach ($redirectsPage->rules()->toStructure() as $rule) {
+                $defaultLang = $kirby->defaultLanguage()?->code() ?? 'fr';
+                $rules = $redirectsPage->content($defaultLang)->rules()->toStructure();
+                foreach ($rules as $rule) {
                     $from = trim($rule->from()->value());
                     if ($from === '') continue;
                     $key    = '/' . trim(strtolower($from), '/');
-                    $target = $rule->to()->toPage();
+                    $target = $rule->to()->toPages()->first();
                     if ($target) {
                         $map[$key] = $target->url();
                     }

site/templates/error.php

@@ -0,0 +1,3 @@
+<?php snippet('header') ?>
+<div id="ssr-content"></div>
+<?php snippet('footer') ?>