feat: update website & init template palette to pass WCAG test; include contrast check in ColorGenerator (#5822)

* docs: update website palette to pass WCAG test

* Darker palette in light mode

* Fix CodeBlock

* Fix front page

* Fix announcement color

* Unify primary color

* Add contrast check in website

* Fix color input not updating

* Use website for preview; allow changing background

* Persist in localStorage

* Fixes

* Fix SSR

* Edit dark mode separately

* Fix light mode palette

* Fix storage reset

* Fix CSS

* Fix

* fix toggling when not on styling-layout

* require 100% lighthouse accessibility score

* use sessionStorage

* refactor

* tweak light color

* update comments

Co-authored-by: sebastienlorber <lorber.sebastien@gmail.com>

.github/workflows/lighthousesrc.json

@@ -1,5 +1,10 @@
 {
   "ci": {
+    "assert": {
+      "assertions": {
+        "categories:accessibility": ["error", {"minScore": 1}]
+      }
+    },
     "collect": {
       "settings": {
         "skipAudits": [