feat: add locale_names and available_locales helpers

Add two new helper functions:
- locale_names($page): returns locale code => display name map,
  with support for site-level overrides via the localeNames config key.
- available_locales($page): returns url key => display name map
  for all active locales, mapping the default locale to an empty key.

These helpers allow sites to remove the localeNames config array and
the locales closure from their config.php, keeping that logic here.

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

src/helpers.php

@@ -117,3 +117,54 @@ function packageDefaultLocale($page = null): string
 {
     return $page->defaultLocale ?? 'en';
 }
+
+/**
+ * Returns the display name map for all supported locales.
+ * Falls back to the locale code if not found.
+ *
+ * Site-level overrides can be provided via a `localeNames` config key.
+ *
+ * @param  mixed  $page
+ * @return array<string, string>  locale code => display name
+ */
+function locale_names($page): array
+{
+    static $defaults = [
+        'en'    => 'English',
+        'cs'    => 'Čeština',
+        'fr'    => 'Français',
+        'nb-NO' => 'Norsk bokmål',
+        'pt'    => 'Português',
+        'pt-BR' => 'Português Brasil',
+        'ta'    => 'தமிழ்',
+    ];
+
+    if (isset($page->localeNames) && is_array($page->localeNames)) {
+        return $page->localeNames;
+    }
+
+    return $defaults;
+}
+
+/**
+ * Returns an ordered map of URL key => display name for all available locales.
+ * The default locale uses an empty string key (no URL prefix).
+ *
+ * Intended for use in navigation language selectors.
+ *
+ * @param  mixed  $page
+ * @return array<string, string>  url key => display name
+ */
+function available_locales($page): array
+{
+    $names = locale_names($page);
+
+    return $page->localization->keys()
+        ->mapWithKeys(function ($locale) use ($page, $names) {
+            $urlKey = ($locale === packageDefaultLocale($page)) ? '' : $locale;
+            $name = $names[$locale] ?? $locale;
+
+            return [$urlKey => $name];
+        })
+        ->all();
+}