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

tools/base_tool.py

@@ -181,6 +181,14 @@ class BaseTool(ABC):
     # --- Verification ---
     user_visible_verification: list[str] = []
 
+    # --- Optional telemetry / quality hints for the scoring engine ---
+    # If set (0.0-1.0), lib/scoring.py uses these directly instead of falling
+    # back to stability-based heuristics. Leave unset unless the tool has a
+    # real measured or well-calibrated value.
+    quality_score: Optional[float] = None
+    historical_success_rate: Optional[float] = None
+    latency_p50_seconds: Optional[float] = None
+
     # ---- Status reporting ----
 
     def get_status(self) -> ToolStatus:
@@ -255,6 +263,9 @@ class BaseTool(ABC):
             "agent_skills": self.agent_skills,
             "related_skills": self.agent_skills,
             "user_visible_verification": self.user_visible_verification,
+            "quality_score": self.quality_score,
+            "historical_success_rate": self.historical_success_rate,
+            "latency_p50_seconds": self.latency_p50_seconds,
         }
 
     # ---- Cost estimation ----