feat(movement): send jump packet to server (opcode 0xF61B)

Build and send GameAction(Jump) with extent + world-space launch
velocity + sequence counters. Wire format from holtburger
JumpActionData::pack. Server can now validate and replicate jumps
to nearby clients.

Also compute RunRate locally via PlayerWeenie.InqRunRate when
running (server doesn't echo UpdateMotion ForwardSpeed to sender).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/AcDream.Core.Net/Messages/JumpAction.cs

@@ -0,0 +1,57 @@
+using System.Numerics;
+using AcDream.Core.Net.Packets;
+
+namespace AcDream.Core.Net.Messages;
+
+/// <summary>
+/// Outbound <c>GameAction(Jump)</c> message — opcode <c>0xF61B</c>.
+/// Sent when the player releases the spacebar to jump. The server uses
+/// the extent + velocity to validate the jump and replicate it to nearby
+/// clients.
+///
+/// Wire layout (from holtburger JumpActionData::pack):
+///   u32 0xF7B1 (GameAction envelope)
+///   u32 sequence
+///   u32 0xF61B (Jump sub-opcode)
+///   f32 extent (0.0–1.0 charge power)
+///   f32 velocity.x, f32 velocity.y, f32 velocity.z
+///   u16 instanceSequence
+///   u16 serverControlSequence
+///   u16 teleportSequence
+///   u16 forcePositionSequence
+///   u32 objectGuid (0 for normal jump)
+///   u32 spellId (0 for normal jump)
+/// </summary>
+public static class JumpAction
+{
+    public const uint GameActionOpcode = 0xF7B1u;
+    public const uint JumpOpcode       = 0xF61Bu;
+
+    public static byte[] Build(
+        uint gameActionSequence,
+        float extent,
+        Vector3 velocity,
+        ushort instanceSequence,
+        ushort serverControlSequence,
+        ushort teleportSequence,
+        ushort forcePositionSequence)
+    {
+        var w = new PacketWriter(48);
+
+        w.WriteUInt32(GameActionOpcode);
+        w.WriteUInt32(gameActionSequence);
+        w.WriteUInt32(JumpOpcode);
+        w.WriteFloat(extent);
+        w.WriteFloat(velocity.X);
+        w.WriteFloat(velocity.Y);
+        w.WriteFloat(velocity.Z);
+        w.WriteUInt16(instanceSequence);
+        w.WriteUInt16(serverControlSequence);
+        w.WriteUInt16(teleportSequence);
+        w.WriteUInt16(forcePositionSequence);
+        w.WriteUInt32(0); // objectGuid — 0 for normal jump
+        w.WriteUInt32(0); // spellId — 0 for normal jump
+
+        return w.ToArray();
+    }
+}