Fix gap #22 and add CinematicRenderer captions + music support

- AGENT_GUIDE.md: add "never read source code" rule — skills are the
  interface, not .py files
- animation.yaml: add Layer 2 skill-first guardrail in assets stage
- video-reference-analyst.md: Step 4b now mandates Layer 2 before Layer 3,
  explicitly forbids reading implementation code
- CinematicRenderer: add TikTok-style CaptionOverlay and separate music
  track support (narration + music as independent audio layers)
- cinematic/types.ts: add CinematicCaptionConfig and music prop types

pipeline_defs/animation.yaml

@@ -198,6 +198,7 @@ stages:
       - "Layer 3 skills read for EVERY generation tool before writing prompts (check agent_skills field)"
       - "Clip duration maximized (prefer 10s over 5s) to reduce API calls and cost"
       - "Use selector tools (video_selector, tts_selector, image_selector) — never call provider tools directly"
+      - "Read Layer 2 skills for each tool BEFORE reading source code — skills contain usage guidance, source code is implementation detail"
     success_criteria:
       - Schema-valid asset_manifest artifact
       - All referenced asset files exist on disk