feat(net): L.3b — capture per-object friction + elasticity from CreateObject

Companion to L.3a (a1c27b3) which ported the velocity-reflection bounce.
Previously the CreateObject parser did `pos += 4` for both Friction and
Elasticity floats — silently dropping the wire data so every entity got
the PhysicsBody constructor default (0.05 elasticity, 0.5 friction).

Server-set bouncier surfaces or stickier objects therefore felt
identical to inert walls on collision. Inelastic projectiles via
PhysicsState bit 0x20000 (already plumbed in Commit A) had no per-
object elasticity to override.

Now the parser captures the floats, surfaces them on Parsed +
EntitySpawn, leaving the values at default (null) when their
PhysicsDescriptionFlag bits aren't set. Subscribers (e.g., the
remote-entity dead-reckoning path, future spell-projectile rendering)
can apply them when they wire elasticity to PhysicsBody.Elasticity.

The local player's PhysicsBody is constructed at controller init,
not from a CreateObject — so this commit alone produces no
user-visible local-player change. Effect lands when remote/projectile
physics consume EntitySpawn.Elasticity.

Files:
- CreateObject.cs:284-294: declare friction + elasticity accumulators.
- CreateObject.cs:467-487: parse floats instead of skipping.
- CreateObject.cs:543-555: propagate to Parsed via both return paths.
- WorldSession.cs:67-71: extend EntitySpawn record.
- WorldSession.cs:665-668: pipe through to subscribers.

Tests: 1491 still pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.Core.Net/WorldSession.cs

@@ -63,7 +63,13 @@ public sealed class WorldSession : IDisposable
         // ObjectDescriptionFlags: retail PWD._bitfield (acclient.h:6431-6463)
         // — drives IsPlayer/IsPK/IsPKLite/IsImpenetrable for PvP gating.
         uint? PhysicsState = null,
-        uint? ObjectDescriptionFlags = null);
+        uint? ObjectDescriptionFlags = null,
+        // L.3b (2026-04-30): per-object physics tuning from the wire.
+        // Friction defaults to PhysicsBody constructor value (0.5f).
+        // Elasticity defaults to 0.05f. When set, drives the velocity-
+        // reflection bounce magnitude (clamped to [0, 0.1] retail-side).
+        float? Friction = null,
+        float? Elasticity = null);
 
     /// <summary>Fires when the session finishes parsing a CreateObject.</summary>
     public event Action<EntitySpawn>? EntitySpawned;
@@ -657,7 +663,9 @@ public sealed class WorldSession : IDisposable
                         parsed.Value.MotionState,
                         parsed.Value.MotionTableId,
                         parsed.Value.PhysicsState,
-                        parsed.Value.ObjectDescriptionFlags));
+                        parsed.Value.ObjectDescriptionFlags,
+                        parsed.Value.Friction,
+                        parsed.Value.Elasticity));
                 }
             }
             else if (op == DeleteObject.Opcode)