fix: declare landing page as light-only to prevent dark theme extension issues

The landing page has no dark mode support, so browser extensions like
Dark Reader force-invert colors and break the design. This adds
color-scheme: light only in both CSS and meta tags, plus a
darkreader-lock meta tag, to signal that the page should not be
auto-darkened.

apps/landing/src/styles/globals.css

@@ -1,5 +1,9 @@
 @import "tailwindcss";
 
+html {
+  color-scheme: light only;
+}
+
 @theme {
   --color-accent: #f59e0b;
   --color-accent-hover: #d97706;