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/services/swf/add-size32.ts

@@ -34,7 +34,8 @@ export function nitroHasSize32(json: Record<string, unknown>): boolean {
 export async function addSize32ToBundle(
 	buffer: Buffer,
 ): Promise<Buffer | null> {
-	const { json, png, jsonFileName } = parseNitroBundle(buffer);
+	const { json, texture, textureFormat, jsonFileName } =
+		parseNitroBundle(buffer);
 	if (nitroHasSize32(json)) return null;
 
 	const name = (json.name as string) || jsonFileName.replace(/\.json$/, "");
@@ -68,7 +69,7 @@ export async function addSize32ToBundle(
 	for (const [frameName, frame] of Object.entries(frames)) {
 		const f = frame.frame;
 		if (!f || f.w <= 0 || f.h <= 0) continue;
-		const { data, info } = await sharp(png)
+		const { data, info } = await sharp(texture)
 			.extract({ left: f.x, top: f.y, width: f.w, height: f.h })
 			.raw()
 			.ensureAlpha()
@@ -95,7 +96,7 @@ export async function addSize32ToBundle(
 		const f = frame.frame;
 		if (f.w <= 0 || f.h <= 0) continue;
 
-		const src = await sharp(png)
+		const src = await sharp(texture)
 			.extract({ left: f.x, top: f.y, width: f.w, height: f.h })
 			.raw()
 			.ensureAlpha()
@@ -131,7 +132,12 @@ export async function addSize32ToBundle(
 
 	if (Object.keys(newAssets).length === 0) return null;
 
-	const { png: newPng, frames: newFrames } = buildSpritesheet(images);
+	// Preserve the source bundle's texture format: regenerating a scale must
+	// not silently downgrade a WebP bundle back to PNG.
+	const { texture: newTexture, frames: newFrames } = await buildSpritesheet(
+		images,
+		{ format: textureFormat },
+	);
 
 	// Update existing frame coordinates (sheet was rebuilt).
 	for (const [frameName, frame] of Object.entries(frames)) {
@@ -171,5 +177,12 @@ export async function addSize32ToBundle(
 		vis.push({ ...sourceVis, size: 32 });
 	}
 
-	return createNitroBundle(json, newPng, name);
+	// Keep the client-facing image pointer aligned with the member
+	// `createNitroBundle` is about to write.
+	const sheet = (json.spritesheet ?? {}) as Record<string, unknown>;
+	const meta = (sheet.meta ?? {}) as Record<string, unknown>;
+	sheet.meta = { ...meta, image: `${name}.${textureFormat}` };
+	json.spritesheet = sheet;
+
+	return createNitroBundle(json, newTexture, name);
 }