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/vips.ts

@@ -0,0 +1,40 @@
+/**
+ * Singleton wrapper for wasm-vips initialization.
+ * wasm-vips requires async initialization, so we cache the instance.
+ */
+
+import type Vips from "wasm-vips";
+
+let vipsInstance: Awaited<ReturnType<typeof Vips>> | null = null;
+let vipsInitPromise: Promise<Awaited<ReturnType<typeof Vips>> | null> | null = null;
+
+/**
+ * Get the initialized wasm-vips instance.
+ * Returns null if wasm-vips is not available or fails to initialize.
+ */
+export async function getVips(): Promise<Awaited<ReturnType<typeof Vips>> | null> {
+	if (vipsInstance) {
+		return vipsInstance;
+	}
+
+	if (vipsInitPromise) {
+		return vipsInitPromise;
+	}
+
+	vipsInitPromise = (async () => {
+		try {
+			const VipsInit = (await import("wasm-vips")).default;
+			vipsInstance = await VipsInit();
+			return vipsInstance;
+		} catch {
+			// wasm-vips not available
+			return null;
+		}
+	})();
+
+	const result = await vipsInitPromise;
+	if (!result) {
+		vipsInitPromise = null; // Allow retry on failure
+	}
+	return result;
+}