fix(studio,runtime,engine,compiler): 8 bug fixes — audio, render, timeline, Lottie, thumbnails, video render (#133)

## Summary

**Original 5 bugs fixed:**

- **Bug 1 — Audio silent after seek**: Added `Accept-Ranges` / `Content-Length` + `206 Partial Content` to the static asset server for byte-range seeking.
- **Bug 2 — Download 404 after restart**: Render list endpoint now registers on-disk renders into the in-memory job map.
- **Bug 3 — Timeline stops at GSAP end**: `resolveRootTimelineFromDocument` pads the GSAP timeline to match `data-duration` when the composition declares longer.
- **Bug 4 — Render stuck at 0%**: Store `jobState` reference (not spread copy) so async progress mutations reach the SSE stream.
- **Bug 5 — Lottie missing in preview/render**: Two fixes — (a) moved Lottie adapter before GSAP so `onUpdate` wins; (b) fixed bundler silently dropping external CDN `\<script src>` tags from sub-compositions (root cause: `$content(s).html()` returns `""` for external scripts).

**3 additional bugs fixed:**

- **Bug 6 — Blank thumbnails outside monorepo**: Implemented `generateThumbnail` in the CLI adapter using Puppeteer.
- **Bug 7 — Video empty in rendered sub-compositions**: Fixed `parseVideoElements` selector from `video[id][src]` to `video[src][data-start]` + auto-assign IDs.
- **Render errors**: Failed renders now show their error message in the renders panel.

## Commits

| Commit | Description |
| --- | --- |
| `3951c6f` | fix(studio): store render job reference instead of snapshot copy |
| `f331c30` | fix(studio): make previously-completed renders downloadable after restart |
| `a5e2d04` | fix(studio): add range request support for audio/video seeking in preview |
| `f24317a` | fix(runtime): pad GSAP timeline to data-duration when composition declares longer duration |
| `7cf38ca` | fix(runtime): fix Lottie adapter conflicting with GSAP-driven animations |
| `bc99209` | fix(studio): surface render error messages in the renders panel |
| `8fc9e8b` | fix(cli): implement generateThumbnail in studio adapter |
| `90277ea` | fix(engine): render videos inside sub-compositions that lack an explicit id |
| `f5bb579` | fix(compiler): preserve external CDN scripts from sub-compositions in bundle |

## Test plan

- [x] `golden-lyric-video`: seek → audio plays from seeked position
- [x] Any project: render → progress advances past 0%, reaches 100%
- [x] Any project: complete render, restart `hyperframes dev`, Download → works
- [x] `intro-vid`: play → runs full 5s (not stopping at 3s)
- [x] `hyperframe-build-up-demo`: play → rocket Lottie visible during 0-2s ✅ verified
- [x] Outside monorepo: Compositions sidebar shows thumbnail images (not blank)
- [x] `bug.zip` project: render → video in polaroid sub-composition appears in output
- [x] Trigger a failed render → error message shown

packages/studio/src/components/ui/VideoFrameThumbnail.tsx

@@ -0,0 +1,54 @@
+import { useState, useEffect, useRef } from "react";
+
+/**
+ * Extracts a representative JPEG frame from a video URL using a hidden
+ * video + canvas. Seeks to ~10% of duration to avoid black opening frames.
+ * Used by AssetThumbnail (assets tab) and RenderQueueItem (renders tab).
+ */
+export function VideoFrameThumbnail({ src }: { src: string }) {
+  const [frame, setFrame] = useState<string | null>(null);
+  const didExtract = useRef(false);
+
+  useEffect(() => {
+    if (didExtract.current) return;
+    didExtract.current = true;
+
+    const video = document.createElement("video");
+    video.crossOrigin = "anonymous";
+    video.muted = true;
+    video.preload = "metadata";
+
+    const canvas = document.createElement("canvas");
+    const ctx = canvas.getContext("2d");
+
+    const cleanup = () => {
+      video.src = "";
+      video.load();
+    };
+
+    video.addEventListener("loadedmetadata", () => {
+      video.currentTime = Math.min(2, video.duration * 0.1 || 2);
+    });
+
+    video.addEventListener("seeked", () => {
+      if (!ctx) return;
+      canvas.width = video.videoWidth;
+      canvas.height = video.videoHeight;
+      ctx.drawImage(video, 0, 0);
+      setFrame(canvas.toDataURL("image/jpeg", 0.7));
+      cleanup();
+    });
+
+    video.addEventListener("error", cleanup);
+    video.src = src;
+    video.load();
+
+    return cleanup;
+  }, [src]);
+
+  if (!frame) {
+    return <div className="w-full h-full bg-neutral-800 animate-pulse" />;
+  }
+
+  return <img src={frame} alt="" draggable={false} className="w-full h-full object-contain" />;
+}