feat: add 'system' inside the theme toggle (#766)

* feat: add 'system' inside the theme toggle

* chore: generate hugo_stats.json

* fix: missing css

* chore: reorganize code

* feat: menu

* chore: simplify

* chore: some i18n

* review

* fix: remove replace

exampleSite/hugo_stats.json

@@ -143,6 +143,7 @@
       "hextra-tabs-panel",
       "hextra-tabs-toggle",
       "hextra-theme-toggle",
+      "hextra-theme-toggle-options",
       "hextra-toc",
       "hide-tail",
       "highlight",
@@ -359,6 +360,7 @@
       "hx:group-[.copied]/copybtn:hidden",
       "hx:group-data-[theme=dark]:hidden",
       "hx:group-data-[theme=light]:hidden",
+      "hx:group-data-[theme=system]:hidden",
       "hx:group-hover/code:opacity-100",
       "hx:group-hover:underline",
       "hx:group-open:before:rotate-90",