feat: add view transform, photo loading and download helpers

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

tests/load-image.test.ts

@@ -0,0 +1,16 @@
+import { describe, expect, it } from 'vitest';
+import { fitSize, MAX_SIDE } from '../src/lib/load-image';
+
+describe('fitSize', () => {
+  it('downscales a 12 MP landscape photo to the max side', () => {
+    expect(fitSize(4000, 3000, MAX_SIDE)).toEqual({ width: 2000, height: 1500 });
+  });
+
+  it('downscales portrait photos by their height', () => {
+    expect(fitSize(3024, 4032, 2000)).toEqual({ width: 1500, height: 2000 });
+  });
+
+  it('never upscales small images', () => {
+    expect(fitSize(800, 600, 2000)).toEqual({ width: 800, height: 600 });
+  });
+});