skills: adopt GSAP Layer 3 + Layer 2 animation-runtime routing

Mirror the official GSAP AI skills (greensock/gsap-skills, MIT) into
.agents/skills/ and add the Layer 2 wiring that makes them discoverable
from a fresh context.

GSAP covers animation needs that Remotion primitives strain at:
per-character text reveals (SplitText), SVG shape morphs (MorphSVG),
curved camera paths (MotionPath), stroke-reveal line drawing (DrawSVG),
layout-to-layout flight (Flip), and custom bezier easings (CustomEase).
Also becomes mandatory day-1 knowledge if we wire in HyperFrames later
(HF uses GSAP timelines as its native animation runtime).

Layer 3 adds (.agents/skills/):
- gsap-core, gsap-timeline, gsap-plugins, gsap-utils
- gsap-react, gsap-performance
- gsap-scrolltrigger, gsap-frameworks (situational)
- gsap/README.md — OpenMontage-specific framing and Remotion-safe usage

Layer 2 wiring (the discovery triggers):
- skills/meta/animation-runtime-selector.md — NEW routing meta-skill.
  Decision matrix covering Remotion primitives, GSAP plugins, framer-
  motion, Lottie, Manim, D3, TerminalScene. Enforces the "keep it
  simple" bias: reach for GSAP only when the plugin genuinely earns
  its bundle weight.
- skills/pipelines/explainer/asset-director.md — references GSAP for
  kinetic typography, multi-step choreography, SVG line draws.
- skills/pipelines/animation/asset-director.md — references GSAP for
  logo morphs, motion paths, FLIP transitions, custom easings.
- skills/pipelines/cinematic/asset-director.md — references GSAP for
  cinematic camera moves, per-char title reveals, prestige easings.
- AGENT_GUIDE.md — adds a categorized Layer 3 skills table so a fresh-
  context agent can find the right skill by what they're trying to do,
  plus a pointer to animation-runtime-selector.md for routing.

Determinism: every GSAP use inside Remotion must drive timeline progress
from useCurrentFrame(), never requestAnimationFrame. Three Remotion-safe
patterns are documented in both the gsap/README and the selector skill.

Attribution: https://github.com/greensock/gsap-skills (MIT).

AGENT_GUIDE.md

@@ -595,6 +595,26 @@ Reading order:
 
 Example: Before calling `kling_video`, read its `agent_skills` → `ai-video-gen` → get Kling-specific prompt structure, camera direction syntax, and quality keywords that the model responds to best.
 
+### Layer 3 skills, by category
+
+The `.agents/skills/` directory is large. When you're not coming in through a tool's `agent_skills` pointer, use this table to find the right file by *what you're trying to do*:
+
+| Category | Skills |
+|---|---|
+| **Composition runtime** | `remotion`, `remotion-best-practices`, `synthetic-screen-recording` (fake terminal/UI demos via Remotion TerminalScene) |
+| **Animation knowledge (generic)** | `gsap-core`, `gsap-timeline`, `gsap-plugins` (SplitText / MorphSVG / DrawSVG / MotionPath / Flip / CustomEase), `gsap-utils`, `gsap-react`, `gsap-performance`, `gsap-scrolltrigger`, `gsap-frameworks`, `framer-motion` (Disney 12 principles), `lottie-bodymovin` (Lottie export) |
+| **Image generation** | `bfl-api`, `flux-best-practices` |
+| **Video generation** | `ai-video-gen`, `ltx2` |
+| **Audio** | `elevenlabs`, `music`, `sound-effects`, `acestep`, `text-to-speech`, `setup-api-key` |
+| **Avatar / lip-sync** | `avatar-video`, `heygen`, `create-video`, `faceswap`, `video-translate`, `speech-to-text`, `agents` |
+| **Capture** | `playwright-recording` (browser flows), `ffmpeg` (post) |
+| **Visualization** | `beautiful-mermaid`, `d3-viz`, `manim-composer`, `manimce-best-practices`, `manimgl-best-practices` |
+| **Media editing** | `video-edit`, `video-download`, `video-understand`, `video_toolkit`, `visual-style` |
+
+**When in doubt, read the category's meta routing file first:**
+- Picking an animation runtime? → `skills/meta/animation-runtime-selector.md` routes between Remotion primitives, GSAP plugins, framer-motion, Lottie, Manim, D3.
+- Picking a screen-recording mode (real capture vs synthetic terminal)? → `pipeline_defs/screen-demo.yaml` + `skills/pipelines/screen-demo/idea-director.md`.
+
 ## Quick Lookup
 
 | Question | Where to look |