Replaces eager imports of map hooks and Leaflet in app.ts with
dynamic-import wrappers (lazyHook / lazyMapHook). Each page-specific
hook now ships as its own esbuild chunk fetched on first mount;
Leaflet is loaded once and shared across every map page. Pages that
never mount these hooks (/submit, /algo, /about, etc.) no longer pay
for them at all.
