feat(net): handle 0xF74E VectorUpdate so remote players' jumps render

Remote-player jumps were silently dropped — we never parsed the
VectorUpdate broadcast that carries the jump launch velocity, so
the remote body's Z velocity stayed at 0 and the jump animation
showed without any vertical motion.

ACE Player.cs:954 enqueues GameMessageVectorUpdate (opcode 0xF74E)
on every jump in addition to the bracketing UpdateMotion. Wire
layout (GameMessageVectorUpdate.cs):

  u32 opcode (= 0xF74E)
  u32 objectGuid
  3xf32 velocity (world-space, post-rotation)
  3xf32 omega
  u16 instanceSequence
  u16 vectorSequence

This commit:

1. Adds VectorUpdate.TryParse + VectorUpdated session event.
2. WorldSession.ProcessDatagram dispatches 0xF74E.
3. GameWindow subscribes via OnLiveVectorUpdated:
   - Sets remote PhysicsBody.Velocity from the wire vector.
   - When velocity.Z > 0.5 m/s, marks the remote as Airborne,
     clears Contact + OnWalkable bits, and enables the Gravity
     state flag — so calc_acceleration returns (0, 0, -9.8) and
     UpdatePhysicsInternal produces a parabolic arc.
4. The per-tick remote update (TickAnimations remote-physics
   block) now SKIPS the "force OnWalkable + apply_current_movement"
   step when Airborne. Otherwise that path stomps the +Z velocity
   each frame — same shape as the bug the local jump hit before
   K-fix7.
5. ResolveWithTransition for remotes now passes
   isOnGround: !rm.Airborne. Mirrors K-fix7's local-player gate —
   airborne resolves must NOT pre-seed the ContactPlane,
   otherwise AdjustOffset's snap-to-plane branch zeroes the
   upward offset.
6. UpdatePosition handler clears the airborne flag and restores
   ground-contact bits, so the server's authoritative re-grounding
   ends the arc cleanly at the new ground location.

ACDREAM_DUMP_MOTION=1 logs each VectorUpdate as
"VU guid=0x... vel=(...) airborne=...".

Tests stay 1222 green. Live verification pending — watch a remote
character jump.

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

src/AcDream.Core.Net/WorldSession.cs

@@ -92,6 +92,17 @@ public sealed class WorldSession : IDisposable
     /// </summary>
     public event Action<EntityPositionUpdate>? PositionUpdated;
 
+    /// <summary>
+    /// Fires when the session parses a 0xF74E VectorUpdate game message.
+    /// ACE broadcasts this whenever a remote entity's velocity / omega
+    /// changes outside the normal UpdatePosition cadence — the canonical
+    /// case is a remote player JUMPING (Player.cs:954
+    /// <c>EnqueueBroadcast(new GameMessageVectorUpdate(this));</c>).
+    /// Subscribers update the remote's PhysicsBody velocity + airborne
+    /// state so the dead-reckoning produces a proper jump arc.
+    /// </summary>
+    public event Action<VectorUpdate.Parsed>? VectorUpdated;
+
     /// <summary>
     /// Fires when the server sends a PlayerTeleport (0xF751) game message,
     /// signalling that the player is entering portal space. The uint payload
@@ -667,6 +678,20 @@ public sealed class WorldSession : IDisposable
                         posUpdate.Value.Velocity));
                 }
             }
+            else if (op == VectorUpdate.Opcode)
+            {
+                // K-fix9 (2026-04-26): server-broadcast remote jump
+                // velocity. ACE Player.cs:954 enqueues this on every
+                // jump in addition to the bracketing UpdateMotion. The
+                // payload's velocity field is the world-space launch
+                // velocity (post-rotation in
+                // GameMessageVectorUpdate.cs:20-24); subscribers feed
+                // it into the remote PhysicsBody so the dead-reckoning
+                // tick can integrate the arc.
+                var parsed = VectorUpdate.TryParse(body);
+                if (parsed is not null)
+                    VectorUpdated?.Invoke(parsed.Value);
+            }
             else if (op == HearSpeech.LocalOpcode || op == HearSpeech.RangedOpcode)
             {
                 // Phase H.1: local/ranged chat. Standalone GameMessage