One-key formula: AI images, TTS narration, auto music, subtitles, and self-review pipeline

Prove that adding one API key (OPENAI_API_KEY) to the zero-key foundation
produces dramatically better videos for ~$0.69 each. Two compositions built:
The Abyss (deep ocean visual essay) and VOID (neural interface product ad).

New tools:
- audio_probe: ffprobe wrapper with probe_duration() helper
- composition_validator: pre-render checks (asset existence, audio-video sync)
- pixabay_music: royalty-free music scraper (no API key needed)
- freesound_music: Freesound API search + download

Remotion upgrades:
- BackgroundImageLayer: AI images behind data scenes with ken-burns + dark overlay
- Gradient support: all 9 components changed from backgroundColor to background CSS
- CaptionOverlay: word spacing fix, WhisperX word-level subtitles
- HeroTitle: reduced overlay opacity so background images show through

Process codified in agent skills:
- compose-director: audio acquisition flow (present user with voice/music/subtitle
  options), mandatory pre-render validation, post-render self-review (extract
  frames + transcribe + inspect + present findings to user)
- scene-director: narration duration budgeting (word budget from video duration)
- remotion skill: pre-render validation section
- TTS tool: now returns audio_duration_seconds in result

README updated with VOID product ad video embed.

README.md

@@ -29,6 +29,12 @@ Turn your AI coding assistant into a full video production studio. Describe what
 
 > **"SIGNAL FROM TOMORROW"** — a cinematic sci-fi trailer fully produced through OpenMontage: concept, script, scene plan, Veo-generated motion clips, soundtrack, and Remotion composition.
 
+<div align="center">
+  <video src="https://github.com/user-attachments/assets/8a6d2cc3-7ad2-46f5-922f-a8e3e5848d9f" width="100%" controls></video>
+</div>
+
+> **"VOID — Neural Interface"** — a product ad produced with just one API key (OpenAI). 4 AI-generated images (gpt-image-1), TTS narration, auto-sourced royalty-free music, word-level subtitles via WhisperX, and Remotion data visualizations. Total cost: **$0.69**. Zero manual asset work.
+
 Works with **Claude Code, Cursor, Copilot, Windsurf, Codex** — any AI coding assistant that can read files and run code.
 
 ---