Replace sharp with wasm-vips for image processing

Fixes #696

- Replaced sharp dependency with wasm-vips (WebAssembly build of libvips)
- Eliminates native build requirements that caused installation failures
- Added vips.ts singleton wrapper for async initialization
- Updated image-resize.ts and image-convert.ts to use wasm-vips API
- Added unit tests for image processing functionality

packages/coding-agent/src/utils/image-convert.ts

@@ -1,3 +1,5 @@
+import { getVips } from "./vips.js";
+
 /**
  * Convert image to PNG format for terminal display.
  * Kitty graphics protocol requires PNG format (f=100).
@@ -11,16 +13,23 @@ export async function convertToPng(
 		return { data: base64Data, mimeType };
 	}
 
+	const vips = await getVips();
+	if (!vips) {
+		// wasm-vips not available
+		return null;
+	}
+
 	try {
-		const sharp = (await import("sharp")).default;
 		const buffer = Buffer.from(base64Data, "base64");
-		const pngBuffer = await sharp(buffer).png().toBuffer();
+		const img = vips.Image.newFromBuffer(buffer);
+		const pngBuffer = img.writeToBuffer(".png");
+		img.delete();
 		return {
-			data: pngBuffer.toString("base64"),
+			data: Buffer.from(pngBuffer).toString("base64"),
 			mimeType: "image/png",
 		};
 	} catch {
-		// Sharp not available or conversion failed
+		// Conversion failed
 		return null;
 	}
 }