feat(net): Phase 6.6 — parse UpdateMotion (0xF74C) into MotionUpdated event

Server sends UpdateMotion whenever an entity's motion state changes:
NPCs starting a walk cycle, creatures switching to a combat stance,
doors opening, a player waving, etc. Phase 6.1-6.4 already handles
rendering different (stance, forward-command) pairs for the INITIAL
CreateObject, but without this message NPCs freeze in whatever pose
they spawned with and never transition to walking/fighting.

Added UpdateMotion.TryParse with the same ServerMotionState the
CreateObject path uses, reached via a slightly different outer
layout (guid + instance seq + header'd MovementData; the MovementData
starts with the 8-byte sequence/autonomous header this time rather
than being preceded by a length field). Only the (stance, forward-
command) pair is extracted — same subset CreateObject grabs.

WorldSession dispatches MotionUpdated(guid, state) when a 0xF74C
body parses successfully. The App-side wiring (guid→entity lookup
and AnimatedEntity cycle swap) is intentionally deferred to a
separate commit because it touches GameWindow which is currently
being edited by the Phase 9.1 translucent-pass work.

89 Core.Net tests (was 83, +6 for UpdateMotion coverage).

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

tests/AcDream.Core.Tests/Meshing/TranslucencyKindTests.cs

@@ -0,0 +1,81 @@
+using AcDream.Core.Meshing;
+using DatReaderWriter.Enums;
+
+namespace AcDream.Core.Tests.Meshing;
+
+/// <summary>
+/// Verifies that <see cref="TranslucencyKindExtensions.FromSurfaceType"/> maps
+/// SurfaceType flag combinations to the correct <see cref="TranslucencyKind"/>
+/// according to the documented priority order:
+///   Additive &gt; InvAlpha &gt; AlphaBlend (Alpha|Translucent) &gt; ClipMap &gt; Opaque
+/// </summary>
+public class TranslucencyKindTests
+{
+    // ── Opaque cases ────────────────────────────────────────────────────────
+
+    [Fact]
+    public void Opaque_FromZeroFlags_ReturnsOpaque()
+        => Assert.Equal(TranslucencyKind.Opaque, TranslucencyKindExtensions.FromSurfaceType((SurfaceType)0));
+
+    [Fact]
+    public void Opaque_FromBase1SolidFlag_ReturnsOpaque()
+        => Assert.Equal(TranslucencyKind.Opaque, TranslucencyKindExtensions.FromSurfaceType(SurfaceType.Base1Solid));
+
+    [Fact]
+    public void Opaque_FromBase1ImageFlag_ReturnsOpaque()
+        => Assert.Equal(TranslucencyKind.Opaque, TranslucencyKindExtensions.FromSurfaceType(SurfaceType.Base1Image));
+
+    // ── ClipMap cases ───────────────────────────────────────────────────────
+
+    [Fact]
+    public void ClipMap_FromBase1ClipMapFlag_ReturnsClipMap()
+        => Assert.Equal(TranslucencyKind.ClipMap, TranslucencyKindExtensions.FromSurfaceType(SurfaceType.Base1ClipMap));
+
+    [Fact]
+    public void ClipMap_WithOtherOpaqueFlags_ReturnsClipMap()
+        => Assert.Equal(TranslucencyKind.ClipMap,
+            TranslucencyKindExtensions.FromSurfaceType(SurfaceType.Base1ClipMap | SurfaceType.Gouraud));
+
+    // ── AlphaBlend cases ────────────────────────────────────────────────────
+
+    [Fact]
+    public void AlphaBlend_FromAlphaFlag_ReturnsAlphaBlend()
+        => Assert.Equal(TranslucencyKind.AlphaBlend, TranslucencyKindExtensions.FromSurfaceType(SurfaceType.Alpha));
+
+    [Fact]
+    public void AlphaBlend_FromTranslucentFlag_ReturnsAlphaBlend()
+        => Assert.Equal(TranslucencyKind.AlphaBlend, TranslucencyKindExtensions.FromSurfaceType(SurfaceType.Translucent));
+
+    [Fact]
+    public void AlphaBlend_FromAlphaAndTranslucentFlags_ReturnsAlphaBlend()
+        => Assert.Equal(TranslucencyKind.AlphaBlend,
+            TranslucencyKindExtensions.FromSurfaceType(SurfaceType.Alpha | SurfaceType.Translucent));
+
+    [Fact]
+    public void AlphaBlend_AlphaWithClipMap_AlphaWins()
+        => Assert.Equal(TranslucencyKind.AlphaBlend,
+            TranslucencyKindExtensions.FromSurfaceType(SurfaceType.Alpha | SurfaceType.Base1ClipMap));
+
+    // ── InvAlpha cases ──────────────────────────────────────────────────────
+
+    [Fact]
+    public void InvAlpha_FromInvAlphaFlag_ReturnsInvAlpha()
+        => Assert.Equal(TranslucencyKind.InvAlpha, TranslucencyKindExtensions.FromSurfaceType(SurfaceType.InvAlpha));
+
+    [Fact]
+    public void InvAlpha_InvAlphaBeatsAlpha()
+        => Assert.Equal(TranslucencyKind.InvAlpha,
+            TranslucencyKindExtensions.FromSurfaceType(SurfaceType.InvAlpha | SurfaceType.Alpha));
+
+    // ── Additive cases ──────────────────────────────────────────────────────
+
+    [Fact]
+    public void Additive_FromAdditiveFlag_ReturnsAdditive()
+        => Assert.Equal(TranslucencyKind.Additive, TranslucencyKindExtensions.FromSurfaceType(SurfaceType.Additive));
+
+    [Fact]
+    public void Additive_AdditiveBeatsAllOther()
+        => Assert.Equal(TranslucencyKind.Additive,
+            TranslucencyKindExtensions.FromSurfaceType(
+                SurfaceType.Additive | SurfaceType.InvAlpha | SurfaceType.Alpha | SurfaceType.Base1ClipMap));
+}