fix: SEO canonical URLs, LCP performance, remove unused dependencies

- Remove duplicate app/projects/ route (was causing 5xx and soft 404)
- Fix nginx: redirect www.dk0.dev → dk0.dev (non-www canonical)
- Fix not-found.tsx: locale-prefixed links, remove framer-motion dependency
- Add fetchPriority='high' and will-change to Hero LCP image
- Add preconnect hints for hardcover.app and cms.dk0.dev
- Reduce background blur from 100px to 80px (LCP rendering delay)
- Remove boneyard-js (~20 KiB), replace with custom Skeleton component
- Remove react-icons (~10 KiB), replace with inline SVGs
- Conditionally render mobile menu (saves ~20 DOM nodes)
- Add /books to sitemap
- Optimize image config with explicit deviceSizes/imageSizes

__mocks__/boneyard-js/react.tsx

@@ -1,6 +0,0 @@
-import React from "react";
-
-export function Skeleton({ children, loading }: { children: React.ReactNode; loading: boolean; name?: string; animate?: string; transition?: boolean | number }) {
-  if (loading) return <div data-testid="boneyard-skeleton">Loading...</div>;
-  return <>{children}</>;
-}