merge head/nav templates into unified head.php + header.php; semantic CSS for nav

public/index.php

@@ -60,13 +60,10 @@ $ogTags = [
     'site_name'   => 'Posterg – ERG',
 ];
 $extraCss = ['/assets/css/main.css'];
+$bodyClass = 'home-body';
 ?>
-<?php include APP_ROOT . '/templates/public/head.php'; ?>
-<body class="home-body">
-    <a href="#main-content" class="skip-link">Aller au contenu principal</a>
-
-    <?php include APP_ROOT . '/templates/nav.php'; ?>
-    <?php include APP_ROOT . '/templates/search-bar.php'; ?>
+<?php include APP_ROOT . '/templates/head.php'; ?>
+    <?php include APP_ROOT . '/templates/header.php'; ?>
 
     <?php if ($year): ?>
     <p class="filter-info" role="status">