feat: free-roam mode + fix multiplayer sync + remote player polish

Backend (ArenaRoom.js):
- Strip race state machine (lobby/countdown/playing/round/qualify). Persistent
  "playing" phase, no rounds, no checkpoints. Free-roam multi.
- Spawn lowered to y=1.5 (was 5) + MIN_DIST raised to 5 (was 3) to avoid
  ejecting overlapping players at connect.
- Schema kept intact (handshake-safe); deprecated fields default-valued.
- npm run schema:gen wired (anti-drift codegen).

Unity client:
- C# schema generated by schema-codegen into RolldSchema namespace
  (Generated/GameState.cs, Generated/Player.cs). NetworkSchema.cs removed —
  handshake no longer scans global namespace.
- NetworkManager: typed Room<GameState>, callbacks rebound, seeds players
  already in room on join.
- RemotePlayerController:
  * Post-spawn 1.5s grace window (BumpReady) — local PlayerController.HandleBump
    ignores remotes during grace.
  * Solid SphereCollider disabled during grace, re-enabled afterwards — fixes
    the kinematic-vs-dynamic eject when a new client spawns inside someone.
  * NPCBall prefab material switched from invisible-in-URP Default-Material to
    BallShader.shadergraph.
  * TrailRenderer added, tinted with player's chosen color.
  * Name label distance-scales (1x-8x) so pseudos remain readable far away.
- GameHUD: OnGUI emptied — race UI (rounds, mode, timer, playersAlive) gone.
- GameCanvas.jsx: BUILD_PREFIX/VERSION bumped for cache-bust.

Frontend WebGL build (pretty_build): final build with all the above.

game/Assets/Scripts/Network/Generated/Player.cs

@@ -0,0 +1,85 @@
+// 
+// THIS FILE HAS BEEN GENERATED AUTOMATICALLY
+// DO NOT CHANGE IT MANUALLY UNLESS YOU KNOW WHAT YOU'RE DOING
+// 
+// GENERATED USING @colyseus/schema 4.0.15
+// 
+
+using Colyseus.Schema;
+#if UNITY_5_3_OR_NEWER
+using UnityEngine.Scripting;
+#endif
+
+namespace RolldSchema {
+	public partial class Player : Schema {
+#if UNITY_5_3_OR_NEWER
+[Preserve]
+#endif
+public Player() { }
+		[Type(0, "float32")]
+		public float x = default(float);
+
+		[Type(1, "float32")]
+		public float y = default(float);
+
+		[Type(2, "float32")]
+		public float z = default(float);
+
+		[Type(3, "float32")]
+		public float vx = default(float);
+
+		[Type(4, "float32")]
+		public float vy = default(float);
+
+		[Type(5, "float32")]
+		public float vz = default(float);
+
+		[Type(6, "float32")]
+		public float rx = default(float);
+
+		[Type(7, "float32")]
+		public float ry = default(float);
+
+		[Type(8, "float32")]
+		public float rz = default(float);
+
+		[Type(9, "float32")]
+		public float rw = default(float);
+
+		[Type(10, "float64")]
+		public double t = default(double);
+
+		[Type(11, "string")]
+		public string name = default(string);
+
+		[Type(12, "float32")]
+		public float colorR = default(float);
+
+		[Type(13, "float32")]
+		public float colorG = default(float);
+
+		[Type(14, "float32")]
+		public float colorB = default(float);
+
+		[Type(15, "float32")]
+		public float avx = default(float);
+
+		[Type(16, "float32")]
+		public float avy = default(float);
+
+		[Type(17, "float32")]
+		public float avz = default(float);
+
+		[Type(18, "boolean")]
+		public bool isEliminated = default(bool);
+
+		[Type(19, "boolean")]
+		public bool isQualified = default(bool);
+
+		[Type(20, "boolean")]
+		public bool isReady = default(bool);
+
+		[Type(21, "int8")]
+		public sbyte checkpointIndex = default(sbyte);
+	}
+}