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

skills/meta/video-reference-analyst.md

@@ -269,9 +269,14 @@ the user paralyzed with equal choices.
 
 **Before ANY asset generation** (sample or full production), the agent MUST:
 
-1. Check the `agent_skills` field on every tool that will be used
-2. Read each referenced skill in `.agents/skills/`
-3. Apply the provider-specific prompting guidance to all generation prompts
+1. Read the **Layer 2 skill** for each tool from `skills/` directory (usage guidance, input schemas, best practices)
+2. Check the `agent_skills` field on every tool that will be used
+3. Read each referenced **Layer 3 skill** in `.agents/skills/` (provider-specific prompting)
+4. Apply the provider-specific prompting guidance to all generation prompts
+
+**NEVER read tool source code (*.py) to understand how to use a tool.**
+Skills exist precisely so the agent doesn't need to read implementation code.
+Layer 2 skills describe *what* and *when*. Layer 3 skills describe *how*.
 
 This is NOT optional. The AGENT_GUIDE says: *"Layer 3 is not optional.
 Every generation tool has an agent_skills field. Read them before writing