feat: add MOV (ProRes 4444) as transparent video output format (#224)

## Summary

- Adds `--format mov` to the render CLI for ProRes 4444 transparent video output
- ProRes 4444 with alpha is the industry standard for transparent video overlays, supported by CapCut, Final Cut, Premiere, DaVinci, and After Effects
- WebM VP9 alpha technically works but is ignored by all major video editors — only browsers decode it
- Adds MOV to the studio export dropdown alongside MP4 and WebM

## Transparency format comparison

| Format | Codec | Alpha | Video editors | Browsers | File size |
| --- | --- | --- | --- | --- | --- |
| **MOV** | ProRes 4444 | Yes | CapCut, Final Cut, Premiere, DaVinci, After Effects | No (won't play in browser) | Large (~5-40 MB) |
| **WebM** | VP9 | Yes | None (shows black) | Chrome, Firefox | Small (~200 KB) |
| **MP4** | H.264 | No | All | All | Small |

> **Note:** ProRes MOV files do not play in Chromium browsers — they are an intermediate/editing format, not a delivery format. Use [rotato.app/tools/transparent-video](https://rotato.app/tools/transparent-video) to verify transparency works correctly.

## Changes

- **CLI**: Add `mov` to `--format` validation, examples, and output path logic
- **Engine**: `getEncoderPreset()` returns ProRes 4444 (`yuva444p10le`) for `mov` format; handle `.mov` in `applyFaststart` and `muxVideoWithAudio`; add `pix_fmt` to streaming encoder ProRes path
- **Producer**: Treat `mov` like `webm` for alpha capture (PNG frames, screenshot mode, `forceScreenshot`)
- **Studio**: Add MOV option to export format dropdown and render queue hook
- **Core**: Add `mov` to studio API types, render route, and mime helpers
- **Tests**: Add encoder preset tests for mov format (42 total, all passing)

## Usage

```bash
hyperframes render --format mov --output overlay.mov
```

## Test plan

- [x] `pnpm build` passes
- [x] `pnpm --filter @hyperframes/engine test` — 42 tests pass (2 new for MOV)
- [x] `oxlint` and `oxfmt` clean on all 12 changed files
- [x] End-to-end local render produces ProRes 4444 (`yuva444p12le`) with working alpha
- [x] Docker render with `--format mov` — ProRes 4444 confirmed via ffprobe
- [x] Studio dropdown shows MOV option in built JS
- [x] Transparency verified with [rotato.app/tools/transparent-video](https://rotato.app/tools/transparent-video)

packages/engine/src/services/chunkEncoder.ts

@@ -23,12 +23,13 @@ export const ENCODER_PRESETS = {
 
 /**
  * Get encoder preset for a given quality and output format.
- * WebM uses VP9 with alpha-capable pixel format; MP4 uses h264.
+ * WebM uses VP9 with alpha-capable pixel format; MP4 uses h264;
+ * MOV uses ProRes 4444 with alpha for editor-compatible transparency.
  */
 export function getEncoderPreset(
   quality: "draft" | "standard" | "high",
-  format: "mp4" | "webm" = "mp4",
-): { preset: string; quality: number; codec: "h264" | "vp9"; pixelFormat: string } {
+  format: "mp4" | "webm" | "mov" = "mp4",
+): { preset: string; quality: number; codec: "h264" | "vp9" | "prores"; pixelFormat: string } {
   const base = ENCODER_PRESETS[quality];
   if (format === "webm") {
     return {
@@ -38,6 +39,14 @@ export function getEncoderPreset(
       pixelFormat: "yuva420p",
     };
   }
+  if (format === "mov") {
+    return {
+      preset: "4444",
+      quality: base.quality,
+      codec: "prores",
+      pixelFormat: "yuva444p10le",
+    };
+  }
   return { ...base, pixelFormat: "yuv420p" };
 }
 
@@ -121,6 +130,7 @@ export function buildEncoderArgs(
     }
   } else if (codec === "prores") {
     args.push("-c:v", "prores_ks", "-profile:v", preset, "-vendor", "apl0");
+    args.push("-pix_fmt", pixelFormat);
     return [...args, "-y", outputPath];
   }
 
@@ -309,7 +319,11 @@ export async function encodeFramesChunkedConcat(
     }
     const startNumber = i * chunkSize;
     const framesInChunk = Math.min(chunkSize, files.length - startNumber);
-    const ext = outputPath.endsWith(".webm") ? ".webm" : ".mp4";
+    const ext = outputPath.endsWith(".webm")
+      ? ".webm"
+      : outputPath.endsWith(".mov")
+        ? ".mov"
+        : ".mp4";
     const chunkPath = join(chunkDir, `chunk_${String(i).padStart(4, "0")}${ext}`);
     const inputPath = join(framesDir, framePattern);
     const inputArgs = [
@@ -415,10 +429,13 @@ export async function muxVideoWithAudio(
   if (!existsSync(outputDir)) mkdirSync(outputDir, { recursive: true });
 
   const isWebm = outputPath.endsWith(".webm");
+  const isMov = outputPath.endsWith(".mov");
   const args = ["-i", videoPath, "-i", audioPath, "-c:v", "copy"];
 
   if (isWebm) {
     args.push("-c:a", "libopus", "-b:a", "128k");
+  } else if (isMov) {
+    args.push("-c:a", "aac", "-b:a", "192k");
   } else {
     args.push("-c:a", "aac", "-b:a", "192k", "-movflags", "+faststart");
   }
@@ -453,8 +470,9 @@ export async function applyFaststart(
   signal?: AbortSignal,
   config?: Partial<Pick<EngineConfig, "ffmpegProcessTimeout">>,
 ): Promise<MuxResult> {
-  // faststart is MP4-only (moves moov atom to file start for streaming)
-  if (outputPath.endsWith(".webm")) {
+  // faststart is MP4-only (moves moov atom to file start for streaming).
+  // WebM and MOV don't need it — skip the re-mux.
+  if (outputPath.endsWith(".webm") || outputPath.endsWith(".mov")) {
     if (inputPath !== outputPath) copyFileSync(inputPath, outputPath);
     return { success: true, outputPath, durationMs: 0 };
   }