refactor: improve width handling and introduce CSS variables (#678)

* 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- Removed the outdated page-width utility partial to streamline the codebase.

* feat: introduce CSS variables for layout widths and update footer/navbar styles

- Added a new configs.css file to define CSS variables for page, navbar, and footer widths.
- Updated footer and navbar partials to utilize the new CSS classes for consistent width management.
- Refactored head-config-css.html to include the new navbar width variable.
- Enhanced the overall styling structure for better maintainability and responsiveness.

* Refactor: Rename configs.css to variables.css and update references

Remove head-config-css.html and update references to use variables.css instead of configs.css

* Update assets/css/variables.css

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update layouts/partials/head.html

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

layouts/partials/utils/page-width.html

@@ -1,27 +0,0 @@
-{{/* Get page width from site configuration */}}
-
-{{/* Default page width */}}
-{{- $pageWidth := "" -}}
-
-{{/* Get page width setting from page front matter or site params */}}
-{{ with .Params.width -}}
-  {{ $pageWidth = . -}}
-{{ else -}}
-  {{ with .Site.Params.page.width -}}
-    {{ $pageWidth = . -}}
-  {{ end -}}
-{{ end -}}
-
-{{- with $pageWidth -}}
-  {{ if eq . "wide" -}}
-    {{ $pageWidth = "hx:max-w-[90rem]" -}}
-  {{ else if eq . "full" -}}
-    {{ $pageWidth = "max-w-full" -}}
-  {{ else -}}
-    {{ $pageWidth = "hx:max-w-screen-xl" -}}
-  {{ end -}}
-{{ else -}}
-  {{ $pageWidth = "hx:max-w-screen-xl" -}}
-{{ end -}}
-
-{{ return $pageWidth }}