perf(images): convert remaining <img> tags to next/image project-wide

Clears every remaining @next/next/no-img-element warning — automatic
responsive srcset, lazy-loading, and format optimization instead of
always loading the original file at full size. Fixed-size icons got
explicit width/height; dynamic-aspect photos got fill inside a
relative wrapper.

app/blog/[slug]/page.tsx

@@ -110,7 +110,7 @@ export default async function BlogDetailPage({
             href="/todo-cards"
             className="group flex items-center gap-6 border border-border rounded-md px-9 py-7 hover:border-brand transition-colors"
           >
-            <img alt="" src="/icon-todo-passend-dazu.png" className="w-16 h-[4.6875rem] shrink-0 object-contain" />
+            <Image alt="" src="/icon-todo-passend-dazu.png" width={64} height={75} className="w-16 h-[4.6875rem] shrink-0 object-contain" />
             <div className="flex-1 min-w-0 flex flex-col gap-2.5">
               <p className="font-bold text-[0.8125rem] text-brand">Passend dazu:</p>
               <div className="flex items-end justify-between gap-4 w-full">