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/app/api/admin/import/furni/batch-regen/route.ts

@@ -199,7 +199,10 @@ export const POST = withAdmin(
 						});
 						try {
 							const swfBuffer = await fs.readFile(swfPath);
-							const conversion = convertSwfToNitro(swfBuffer, baseClassname);
+							const conversion = await convertSwfToNitro(
+								swfBuffer,
+								baseClassname,
+							);
 							await fs.writeFile(nitroPath, conversion.bundle);
 
 							// Build FurnitureData entry if missing

src/app/api/admin/import/furni/nitro-editor/route.ts

@@ -104,13 +104,16 @@ export const PUT = withAdmin(
 
 		const saved = await withFurniDataLock(async () => {
 			const existingBuffer = await fs.readFile(nitroPath);
-			const { png, json: currentMetadata } = parseNitroBundle(existingBuffer);
+			const { texture, json: currentMetadata } =
+				parseNitroBundle(existingBuffer);
 			if (
 				JSON.stringify(currentMetadata.catalogStudio) !==
 				JSON.stringify(metadata.catalogStudio)
 			)
 				return false;
-			const newBundle = createNitroBundle(metadata, png, base);
+			// `texture` keeps its original encoding, so editing metadata never
+			// changes the bundle's texture format.
+			const newBundle = createNitroBundle(metadata, texture, base);
 			await fs.writeFile(nitroPath, newBundle);
 			return true;
 		});

src/app/api/admin/import/furni/route.ts

@@ -775,7 +775,7 @@ export const PATCH = withAdmin(
 			// Convert SWF → Nitro + update FurnitureData.json
 			try {
 				const swfBuffer = await fs.readFile(swfPath);
-				const conversion = convertSwfToNitro(swfBuffer, baseClassname);
+				const conversion = await convertSwfToNitro(swfBuffer, baseClassname);
 				await fs.writeFile(nitroPath, conversion.bundle);
 
 				// Add to FurnitureData.json if not already present

src/app/api/admin/studio/nitro-quality/route.ts

@@ -4,6 +4,7 @@ import sharp from "sharp";
 import { apiError, apiOk } from "@/lib/api";
 import { withAdmin } from "@/lib/api-handler";
 import {
+	buildNitroCompressionReport,
 	inspectNitroScales,
 	object,
 	resolveNitroFrame,
@@ -21,10 +22,11 @@ export const GET = withAdmin(
 		const base = String(classname).split("*")[0],
 			{ nitroDir } = await getFurniAssetDirs();
 		try {
-			const { json, png } = parseNitroBundle(
+			const parsed = parseNitroBundle(
 				await fs.readFile(path.join(nitroDir, `${base}.nitro`)),
 			);
-			const image = await sharp(png).metadata();
+			const { json, texture } = parsed;
+			const image = await sharp(texture).metadata();
 			if (!image.width || !image.height)
 				return apiError("Invalid bundle texture", 422);
 			const asset = request.nextUrl.searchParams.get("asset");
@@ -33,7 +35,7 @@ export const GET = withAdmin(
 					return apiError("Sprite not found", 404);
 				const resolved = resolveNitroFrame(json, asset),
 					rect = object(resolved.frame.frame);
-				let pipeline = sharp(png).extract({
+				let pipeline = sharp(texture).extract({
 					left: Number(rect.x),
 					top: Number(rect.y),
 					width: Number(rect.w),
@@ -51,7 +53,10 @@ export const GET = withAdmin(
 				});
 			}
 			return apiOk({
-				report: inspectNitroScales(json, image.width, image.height),
+				report: {
+					...inspectNitroScales(json, image.width, image.height),
+					compression: await buildNitroCompressionReport(parsed),
+				},
 			});
 		} catch (error) {
 			if ((error as NodeJS.ErrnoException).code === "ENOENT")