feat(B.6 slice 1): DebugPanel mirror for ProbeAutoWalk checkbox

Wires PhysicsDiagnostics.ProbeAutoWalkEnabled into the DebugVM + ImGui
panel checkbox alongside the existing Probe Resolve / Probe Cell /
Probe BSP hits checkboxes. Following the L.2a + L.2d pattern: the
panel toggle takes effect live (no relaunch needed) because the
diagnostic call sites read the static flag every frame.

Lets the next B.6 trace session toggle the probe via panel checkbox
when ACDREAM_DEVTOOLS=1, without an env-var dance.

src/AcDream.UI.Abstractions/Panels/Debug/DebugVM.cs

@@ -275,6 +275,21 @@ public sealed class DebugVM
         set => PhysicsDiagnostics.ProbeBuildingEnabled = value;
     }
 
+    /// <summary>
+    /// B.6 slice 1 (2026-05-14). Runtime mirror of
+    /// <c>PhysicsDiagnostics.ProbeAutoWalkEnabled</c> (env var
+    /// <c>ACDREAM_PROBE_AUTOWALK</c>). Toggling here flips the
+    /// <c>[autowalk-out]</c> / <c>[autowalk-mt]</c> / <c>[autowalk-up]</c>
+    /// trace used to characterize ACE's behavior during a server-
+    /// initiated auto-walk (issue #63). Low volume when off — only the
+    /// local player's events are filtered through the probe.
+    /// </summary>
+    public bool ProbeAutoWalk
+    {
+        get => PhysicsDiagnostics.ProbeAutoWalkEnabled;
+        set => PhysicsDiagnostics.ProbeAutoWalkEnabled = value;
+    }
+
     // ── Action hooks invoked by panel buttons ──────────────────────────
 
     /// <summary>