Fix automatic readable text contrast for public and admin themes.

Derive admin/public text colors from WCAG contrast, unify ThemeVars CSS emission, and keep navbar overrides in sync with readable vars.

Co-authored-by: Cursor <[email protected]>

src/app/globals.css

@@ -86,12 +86,7 @@
 	--border-subtle: color-mix(in srgb, var(--color-text-muted) 18%, transparent);
 }
 
-/* Dark mode colors are generated by ThemeVars from the selected preset. */
-html.dark {
-	--color-text-readable: var(--color-text);
-	--color-text-muted-readable: var(--color-text-muted);
-	--color-navbar-text-readable: var(--color-navbar-text);
-}
+/* Dark mode colors + readable contrast vars are generated by ThemeVars. */
 html.dark input,
 html.dark select,
 html.dark textarea {