feat(gacha): add /api/gacha wish animation rendered as MP4

A meteor coloured by rarity falls across a night sky, lands in a white
flash, and the label is revealed with its stars popping in. The caller
picks the result and rarity; the route only draws it. Renders as silent
H.264 so Telegram plays it as an animation without GIF banding, and
shares the render slots with /api/gif.

renderer/scripts/render-fixtures.js

@@ -1,5 +1,6 @@
 import {mkdir, writeFile} from 'node:fs/promises';
 import path from 'node:path';
+import {renderGachaVideo} from '../src/render/render-gacha.js';
 import {renderWheelGif} from '../src/render/render-gif.js';
 
 const smoke = process.argv.includes('--smoke');
@@ -47,9 +48,27 @@ const fixtures = [
 
 await mkdir(fixturesDir, {recursive: true});
 
-for (const fixture of smoke ? fixtures.slice(0, 1) : fixtures) {
-  const result = await renderWheelGif(fixture.request, {timeoutInMilliseconds: 30000});
-  const output = path.join(fixturesDir, `${fixture.name}.gif`);
+/** @type {{name: string, request: import('../src/schemas/gacha-request.js').GachaRenderRequest}[]} */
+const gachaFixtures = [
+  {name: 'gacha-5-star', request: {label: 'Pizza', rarity: 5, fps: 24, width: 640}},
+  {name: 'gacha-4-star', request: {label: 'Phở bò tái nạm gầu', rarity: 4, fps: 24, width: 640}},
+  {name: 'gacha-3-star', request: {label: 'Cơm tấm', rarity: 3, fps: 24, width: 854}},
+];
+
+/**
+ * @param {string} name
+ * @param {{buffer: Buffer, byteLength: number, durationMs: number}} result
+ */
+const save = async (name, result) => {
+  const output = path.join(fixturesDir, name);
   await writeFile(output, result.buffer);
-  console.log(`${fixture.name}: ${output} ${result.byteLength} bytes ${result.durationMs}ms`);
+  console.log(`${name}: ${output} ${result.byteLength} bytes ${result.durationMs}ms`);
+};
+
+for (const fixture of smoke ? fixtures.slice(0, 1) : fixtures) {
+  await save(`${fixture.name}.gif`, await renderWheelGif(fixture.request, {timeoutInMilliseconds: 30000}));
+}
+
+for (const fixture of smoke ? gachaFixtures.slice(0, 1) : gachaFixtures) {
+  await save(`${fixture.name}.mp4`, await renderGachaVideo(fixture.request, {timeoutInMilliseconds: 30000}));
 }