Add shared-scene 2D authoring, sprite animation and Rapier2D physics

docs/SCRIPT_API.json

@@ -3,16 +3,19 @@
   "api": {
     "state": "Persistent per-instance mutable data during one play run",
     "params": "Field defaults + component.script.params",
-    "input": "{x,z,attack,pointer,aim,jump,dash,sprint,jumpPressed,dashPressed,resetPressed,yaw,pitch}; yaw=0 faces -Z in first person",
+    "input": "{x,y,z,attack,pointer,aim,jump,dash,sprint,jumpPressed,dashPressed,resetPressed,yaw,pitch}; yaw=0 faces -Z in first person",
     "get": "api.get(id?) -> clone of entity or null",
     "entities": "api.entities() -> clones of entity states",
     "position": "api.position(id?) -> local coordinates",
     "move": "api.move([dx,dy,dz]); real collisions for kinematic body",
     "physics": "api.physics(id?) -> {grounded,velocity:{x,y,z},contacts:[{entityId,normal:[x,y,z]}]}",
-    "velocity": "api.velocity({x?,y?,z?,gravityScale?}); persistent m/s, requires character component; gravity runs at 60 Hz",
+    "velocity": "api.velocity({x?,y?,z?,gravityScale?}); persistent m/s, requires 3D character or any body2d; 2D uses x/y. Gravity runs at 60 Hz",
     "teleport": "api.teleport([x,y,z],yaw?); clears velocity and contacts for character respawn",
     "emit": "api.emit(name,data?); delivers a presentation event to runtime callbacks",
     "rotate": "api.rotate(yRadians)",
+    "rotate2D": "api.rotate2D(zRadians)",
+    "impulse2D": "api.impulse2D([x,y]); applies impulse to dynamic body2d",
+    "collision2d": "Optional behavior hook collision2d(api,event): {entityId,otherId,started,sensor}. Runs before update.",
     "patch": "api.patch(id,patch); updates state/transform/enabled. Structural mesh/collider edits take effect next Play.",
     "animate": "api.animate(clipOrState,loop=true); use false for a one-shot animation",
     "effect": "api.effect(\"swing\"|\"hit\",id?)",