refactor: update page width handling and CSS structure

- Changed the default page width from 1280px to 80rem in hugo.yaml.
- Replaced dynamic page width partials with a new CSS class 'hextra-max-page-width' across multiple layout files for consistency.
- Introduced a new head-config-css.html partial for managing CSS styles related to page width.
- Removed the outdated page-width utility partial to streamline the codebase.

layouts/partials/head-config-css.html

@@ -0,0 +1,15 @@
+{{- $pageWidth := .Site.Params.page.width | default .Params.width -}}
+{{- $maxPageWidth := cond (eq $pageWidth "wide") "90rem" (cond (eq $pageWidth "full") "100%" "80rem") -}}
+
+<style>
+:root {
+  --hextra-max-page-width: {{ $maxPageWidth }};
+}
+
+.hextra-max-page-width {
+  width: 100%;
+  max-width: var(--hextra-max-page-width);
+  margin-left: auto;
+  margin-right: auto;
+}
+</style>