feat(nitro): convert imported SWF bundles to WebP Lossless

Newly converted .nitro bundles now store their spritesheet as WebP VP8L
instead of PNG, so imports land much smaller without changing a single
pixel. The texture member and spritesheet.meta.image are both labelled
from the actual bytes, never from a caller's assumption.

- encode through sharp with lossless and exact, so colour hidden under
  alpha 0 survives; this mirrors ImageSharp's TransparentColorMode.Preserve
- detect PNG/WebP by magic bytes and reject anything the client cannot
  render, on create, download and upload paths
- keep the source format when deriving size-32 sheets, scaling composites
  and editing metadata, so existing bundles are never silently rewritten
- report fidelity in the studio: the compression panel re-encodes with the
  same options the importer uses, so it cannot drift and invent false
  warnings, and shows PNG/WebP size estimates

convertSwfToNitro and buildSpritesheet are now async, so the worker, the
main-thread fallback and every import call site await them. PNG stays
supported for existing bundles and icon sidecars are untouched.

src/lib/furni/nitro-scale32.ts

@@ -45,7 +45,7 @@ export async function generateScale32(input: Buffer): Promise<{
 	count: number;
 	skipped: number;
 }> {
-	const { json, png } = parseNitroBundle(input);
+	const { json, texture, textureFormat } = parseNitroBundle(input);
 	const assets = object(json.assets),
 		sheet = object(json.spritesheet),
 		frames = object(sheet.frames);
@@ -67,7 +67,7 @@ export async function generateScale32(input: Buffer): Promise<{
 	if (!names.length)
 		throw Error("No supported scale 64 furniture sprites were found");
 	if (names.length > 10000) throw Error("Too many sprites to generate safely");
-	const dimensions = await sharp(png).metadata();
+	const dimensions = await sharp(texture).metadata();
 	if (!dimensions.width || !dimensions.height) throw Error("Invalid texture");
 	const images: {
 		id: number;
@@ -103,7 +103,7 @@ export async function generateScale32(input: Buffer): Promise<{
 		}
 		const frame = resolved.frame,
 			rect = object(frame.frame);
-		let sprite = await sharp(png)
+		let sprite = await sharp(texture)
 			.extract({
 				left: Number(rect.x),
 				top: Number(rect.y),
@@ -149,25 +149,35 @@ export async function generateScale32(input: Buffer): Promise<{
 		});
 	}
 	if (!images.length) throw Error("No independent texture frames were found");
-	const atlas = buildSpritesheet(images);
+	const atlas = await buildSpritesheet(images, { format: textureFormat });
 	const width = Math.max(dimensions.width, atlas.width),
 		height = dimensions.height + atlas.height;
 	if (width * height > 64_000_000)
 		throw Error("Combined texture exceeds the texture budget");
-	const combined = await sharp({
+	// The merged sheet must keep the source bundle's texture format so an
+	// existing PNG bundle is not silently converted (or vice versa).
+	const composited = sharp({
 		create: {
 			width,
 			height,
 			channels: 4,
 			background: { r: 0, g: 0, b: 0, alpha: 0 },
 		},
-	})
-		.composite([
-			{ input: png, left: 0, top: 0 },
-			{ input: atlas.png, left: 0, top: dimensions.height },
-		])
-		.png()
-		.toBuffer();
+	}).composite([
+		{ input: texture, left: 0, top: 0 },
+		{ input: atlas.texture, left: 0, top: dimensions.height },
+	]);
+	const combined =
+		textureFormat === "webp"
+			? await composited
+					.webp({
+						lossless: true,
+						nearLossless: false,
+						smartSubsample: false,
+						effort: 6,
+					})
+					.toBuffer()
+			: await composited.png().toBuffer();
 	const generated = new Map<string, boolean>();
 	for (const name of names)
 		if (!skipped.has(name)) generated.set(scaleName(name), true);
@@ -198,7 +208,13 @@ export async function generateScale32(input: Buffer): Promise<{
 	json.spritesheet = {
 		...sheet,
 		frames,
-		meta: { ...object(sheet.meta), size: { w: width, h: height } },
+		meta: {
+			...object(sheet.meta),
+			// Keep the client-facing image pointer aligned with the member
+			// `createNitroBundle` is about to write.
+			image: `${String(json.name || "furniture")}.${textureFormat}`,
+			size: { w: width, h: height },
+		},
 	};
 	json.catalogStudio = {
 		...object(json.catalogStudio),