feat: add view transform, photo loading and download helpers

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib/load-image.ts

@@ -0,0 +1,21 @@
+import type { RasterImage } from './types';
+
+export const MAX_SIDE = 2000;
+
+export function fitSize(width: number, height: number, maxSide: number): { width: number; height: number } {
+  const s = Math.min(1, maxSide / Math.max(width, height));
+  return { width: Math.round(width * s), height: Math.round(height * s) };
+}
+
+export async function loadPhoto(file: Blob): Promise<RasterImage> {
+  const bitmap = await createImageBitmap(file, { imageOrientation: 'from-image' });
+  try {
+    const { width, height } = fitSize(bitmap.width, bitmap.height, MAX_SIDE);
+    const canvas = new OffscreenCanvas(width, height);
+    const ctx = canvas.getContext('2d')!;
+    ctx.drawImage(bitmap, 0, 0, width, height);
+    return { width, height, data: ctx.getImageData(0, 0, width, height).data };
+  } finally {
+    bitmap.close();
+  }
+}