feat: make AI background removal optional with resize-only upload and batch detour selection

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/client/imageResizer.ts

@@ -0,0 +1,15 @@
+export async function resizeToSquare(blob: Blob, size = 1000): Promise<Blob> {
+  const img = await createImageBitmap(blob)
+  const canvas = new OffscreenCanvas(size, size)
+  const ctx = canvas.getContext('2d')!
+  ctx.fillStyle = '#ffffff'
+  ctx.fillRect(0, 0, size, size)
+  const scale = Math.min(size / img.width, size / img.height)
+  const w = img.width * scale
+  const h = img.height * scale
+  const x = (size - w) / 2
+  const y = (size - h) / 2
+  ctx.drawImage(img, x, y, w, h)
+  img.close()
+  return canvas.convertToBlob({ type: 'image/jpeg', quality: 0.92 })
+}