videoSrc prop passes public/ prefix to staticFile(), causing a Remotion TypeError

In tools/video/remotion_caption_burn.py, _render_remotion() builds props["videoSrc"] as f"public/talking-head/{video_filename}". Remotion's staticFile() explicitly rejects paths that include the public/ prefix (it expects a path relative to public/). This causes every render to fail with TypeError: Do not include the public/ prefix when using staticFile().

Fix: drop the prefix — f"talking-head/{video_filename}".