fix(animation): preserve wire motion on every spawn path

Replace the door-specific static-animation seed with one retail description-then-enter-world initializer shared by normal and reactive spawns. This preserves authoritative Dead and On/Off states, prevents replacement corpses from returning to Ready, and pins the lifecycle with Core and App tests.

Co-Authored-By: Codex <codex@openai.com>

src/AcDream.App/Rendering/SpawnMotionInitializer.cs

@@ -0,0 +1,63 @@
+using AcDream.Core.Net.Messages;
+using AcDream.Core.Physics;
+using DatReaderWriter.DBObjs;
+
+namespace AcDream.App.Rendering;
+
+/// <summary>
+/// Builds the initial motion-table state for a server CreateObject using the
+/// same description-then-enter-world lifecycle as retail.
+/// </summary>
+/// <remarks>
+/// Retail oracle: <c>ACCObjectMaint::CreateObject</c> (0x00558870) calls
+/// <c>CPhysicsObj::set_description</c> (0x00514F40), which applies the wire
+/// MovementData. <c>SmartBox::HandleCreateObject</c> (0x00454C80) then calls
+/// <c>CPhysicsObj::enter_world</c> (0x00516170), reaching
+/// <c>CPartArray::HandleEnterWorld</c> (0x00517D70) and
+/// <c>MotionTableManager::HandleEnterWorld</c> (0x0051BDD0).
+/// </remarks>
+internal static class SpawnMotionInitializer
+{
+    internal readonly record struct Plan(uint Style, uint Motion);
+
+    public static AnimationSequencer Create(
+        Setup setup,
+        MotionTable motionTable,
+        IAnimationLoader loader,
+        CreateObject.ServerMotionState? wireState)
+    {
+        var sequencer = new AnimationSequencer(setup, motionTable, loader);
+        Plan plan = ResolvePlan(motionTable, wireState);
+
+        // set_description: install the table default, then apply MovementData.
+        sequencer.InitializeState();
+        sequencer.SetCycle(plan.Style, plan.Motion);
+
+        // enter_world: discard description-time transition links so the first
+        // rendered pose is the server-authored persistent cycle. A corpse's
+        // NonCombat+Dead therefore starts fallen; a door's NonCombat+On/Off
+        // comes from the same wire path with no object-type special case.
+        sequencer.Manager.HandleEnterWorld();
+        return sequencer;
+    }
+
+    internal static Plan ResolvePlan(
+        MotionTable motionTable,
+        CreateObject.ServerMotionState? wireState)
+    {
+        uint style = wireState is { Stance: > 0 } state
+            ? 0x80000000u | state.Stance
+            : (uint)motionTable.DefaultStyle;
+
+        uint motion = MotionCommand.Ready;
+        if (wireState?.ForwardCommand is ushort command && command > 0)
+        {
+            uint resolved = MotionCommandResolver.ReconstructFullCommand(command);
+            motion = resolved != 0
+                ? resolved
+                : 0x40000000u | command;
+        }
+
+        return new Plan(style, motion);
+    }
+}