perf(tasks): show completion sticker instantly

Roll the sticker client-side and render the popup immediately on completion
instead of waiting for the POST roundtrip + DB writes to return it. Preload
the sticker image so the cat is decoded before the bounce-in finishes. The
chosen stickerId is sent to the server, which persists it (falling back to a
server-side roll if missing/invalid).

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.95.2",
+	"version": "1.95.4",
 	"private": true,
 	"type": "module",
 	"scripts": {
@@ -8,7 +8,7 @@
 		"dev": "vite dev",
 		"prebuild": "bash scripts/subset-emoji-font.sh && pnpm exec vite-node scripts/generate-mystery-verses.ts && pnpm exec vite-node scripts/download-models.ts && pnpm exec vite-node scripts/generate-loyalty-cards.ts && pnpm exec vite-node scripts/generate-error-quotes.ts && pnpm exec vite-node scripts/build-hikes.ts && pnpm exec vite-node scripts/build-private-images.ts",
 		"build": "vite build",
-		"postbuild": "pnpm exec vite-node scripts/build-error-page.ts",
+		"postbuild": "pnpm exec vite-node scripts/build-error-page.ts && pnpm exec vite-node scripts/precompress.ts",
 		"preview": "vite preview",
 		"check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
 		"check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",