Zero-key video formula: fix rendering bugs, add 8 demo compositions, update skills

Fix ComparisonCard and CalloutBox dark-theme passthrough in SceneRenderer.
Add 8 demo-props JSON files (3 fixed originals + 5 new compositions).
Update scene-director and compose-director skills with all 10 Remotion
scene types and zero-key rendering guidance. Document the proven
all-dark-background formula in remotion.md. Add cinematic renderer,
onboarding skill, prompt gallery, and demo render script.

AGENT_GUIDE.md

@@ -4,6 +4,16 @@ Start here. This is the complete operating guide and agent contract for OpenMont
 
 For architecture, key files, and conventions see [`PROJECT_CONTEXT.md`](PROJECT_CONTEXT.md).
 
+## First Interaction — Onboarding
+
+When the user's first message is vague, exploratory, or asks what you can do ("make me a video", "what can you do?", "help me create something", "I want to make content"), read the onboarding skill **before** doing anything else:
+
+**Read:** `skills/meta/onboarding.md`
+
+This skill teaches you to run discovery, classify the user's setup, present capabilities in plain language, and offer starter prompts tailored to their available tools. The goal: get the user from "curious" to "making a video" in under 60 seconds.
+
+**Skip onboarding** when the user arrives with a specific, actionable request (e.g., "Make a 60-second explainer about black holes"). Go directly to Rule Zero.
+
 ## Rule Zero — All Production Goes Through a Pipeline
 
 **Every video production request MUST go through the pipeline system. No exceptions.**