video-gen: adopt Seedance 2.0 as preferred premium default

Seedance 2.0 is now routed as the top-ranked video generator whenever a
premium gateway is available. Touches the tool layer, scoring engine,
cinematic pipeline, and both skill layers so discovery works from every
entry point.

- tools/video/seedance_video: BETA stability, quality_score=0.95, add
  reference_to_video operation plus 9 img + 3 vid + 3 audio ceilings,
  fix pre-existing upload_image_fal import
- tools/base_tool: surface optional quality_score / success_rate /
  latency fields in get_info so the scorer can read them
- lib/scoring: fix reliability enum-vs-string bug that was pinning every
  available tool to 0.0, switch to overlap coefficient so rich best_for
  descriptions aren't penalized, add premium-cinematic feature bonus
- pipeline_defs/cinematic + cinematic asset-director: add pixabay_music
  and freesound_music, restore pixabay-first music default
- cinematic compose-director: mandatory Remotion preflight at stage entry
- New Layer 3 .agents/skills/seedance-2-0/SKILL.md (8-part prompt
  structure, multi-shot, lip-sync, reference-to-video, provider landscape)
- New Layer 2 skills/creative/prompting/seedance-prompting.md
- Update ai-video-gen, video-gen-prompting, AGENT_GUIDE, INDEX to flag
  Seedance 2.0 as the preferred premium default and make the skill
  discoverable from every routing path

skills/INDEX.md

@@ -92,6 +92,7 @@ Key capability families to look for in the output:
 | Data Visualization | `creative/data-visualization.md` | Chart type selection, animation, label placement | `d3-viz`, `remotion-best-practices` |
 | Video Stitching | `creative/video-stitching.md` | Multi-clip assembly, AI clip chaining, spatial composition | `ffmpeg`, `video_toolkit` |
 | Video Gen Prompting | `creative/video-gen-prompting.md` | Universal video generation prompt vocabulary | `ai-video-gen`, `ltx2`, `create-video` |
+| ↳ Seedance Prompting | `creative/prompting/seedance-prompting.md` | **Preferred premium default.** Seedance 2.0 8-component structure, multi-shot, lip-sync, reference-to-video | `seedance-2-0`, `ai-video-gen` |
 | ↳ Grok Prompting | `creative/prompting/grok-prompting.md` | Grok image/video prompting, edit flows, reference-image video | `grok-media` |
 | ↳ Sora Prompting | `creative/prompting/sora-prompting.md` | Sora 2 structured template, advanced fields | `ai-video-gen` |
 | ↳ VEO Prompting | `creative/prompting/veo-prompting.md` | VEO 3.1 14-component structure, art movements | `ai-video-gen` |
@@ -306,4 +307,5 @@ Claude Code accesses them via symlinks in `.claude/skills/`.
 | **Animation** | `framer-motion`, `lottie-bodymovin` | `pproenca/dot-skills`, `dylantarre/animation-principles` |
 | **Design** | `tailwind-design-system`, `web-design-guidelines`, `vercel-react-best-practices`, `vercel-composition-patterns` | `wshobson/agents`, `vercel-labs/agent-skills` |
 | **AI Video (HeyGen)** | `heygen`, `avatar-video`, `create-video`, `faceswap`, `ai-video-gen`, `video-download`, `video-edit`, `video-translate`, `video-understand`, `visual-style` | `heygen-com/skills` |
+| **AI Video (Premium)** | `seedance-2-0` — preferred premium default (cinematic, trailer, multi-shot, lip-sync, synced audio); accessed via `seedance_video` (fal.ai) or `heygen_video` Avatar Shots | Local OpenMontage skill |
 | **Infrastructure** | `acestep`, `ltx2`, `playwright-recording` | `digitalsamba/claude-code-video-toolkit` |