fix(anim): left-side motion fallback to right-side animation

AC MotionTables typically define cycles for TurnRight and SideStepRight
but not TurnLeft/SideStepLeft — the left variants reuse the right-side
animation played in reverse. When the left-side command doesn't resolve
to a cycle, fall back to the right-side equivalent so the player isn't
stuck in idle pose.

Fallback map:
  TurnLeft (0x000E) → TurnRight (0x000D)
  SideStepLeft (0x0010) → SideStepRight (0x000F)
  WalkBackward (0x0006) → WalkForward (0x0005)

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

src/AcDream.App/Rendering/GameWindow.cs

@@ -2054,6 +2054,28 @@ public sealed class GameWindow : IDisposable
             stanceOverride: NonCombatStance,
             commandOverride: cmdOverride);
 
+        // AC reuses right-side animations for left-side motions (played in
+        // reverse). If the left-side command has no cycle, fall back to the
+        // right-side equivalent so the player isn't stuck in idle.
+        if (cycle is null || cycle.Framerate == 0f || cycle.HighFrame <= cycle.LowFrame)
+        {
+            ushort fallback = cmdOverride switch
+            {
+                0x000E => 0x000D,  // TurnLeft → TurnRight
+                0x0010 => 0x000F,  // SideStepLeft → SideStepRight
+                0x0006 => 0x0005,  // WalkBackward → WalkForward
+                _ => (ushort)0,
+            };
+            if (fallback != 0)
+            {
+                cycle = AcDream.Core.Meshing.MotionResolver.GetIdleCycle(
+                    ae.Setup, _dats,
+                    motionTableIdOverride: _playerMotionTableId,
+                    stanceOverride: NonCombatStance,
+                    commandOverride: fallback);
+            }
+        }
+
         if (cycle is null || cycle.Framerate == 0f || cycle.HighFrame <= cycle.LowFrame) return;
 
         // If the entity has a sequencer, use SetCycle for transition-link-aware