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/components/Divider.tsx

@@ -1,3 +1,4 @@
+import Image from "next/image";
 import { Reveal } from "./Reveal";
 
 function Word({ children }: { children: string }) {
@@ -16,7 +17,7 @@ function Arrow() {
     <div className="flex items-center justify-center shrink-0">
       <div className="-scale-y-100 rotate-180">
         <div className="relative" style={{ height: "var(--divider-arrow-h)", width: "var(--divider-arrow-w)" }}>
-          <img alt="" src="/icon-separator.svg" className="absolute inset-0 w-full h-full" />
+          <Image alt="" src="/icon-separator.svg" fill sizes="48px" />
         </div>
       </div>
     </div>
@@ -60,7 +61,7 @@ export function Divider() {
               className="relative"
               style={{ height: "var(--divider-sparkle-inner-h)", width: "var(--divider-sparkle-inner-w)" }}
             >
-              <img alt="" src="/icon-separator-right.svg" className="absolute inset-0 w-full h-full" />
+              <Image alt="" src="/icon-separator-right.svg" fill sizes="48px" />
             </div>
           </div>
         </div>