fix(rendering): bound portal resource lifetime

Separate logical ownership, render publication, and GPU retirement across live entities, landblocks, particles, textures, mesh arenas, portal/UI teardown, and per-frame scratch storage. Add bounded DAT/texture caches, upload budgets, three-frame fence retirement, exact-incarnation appearance reconciliation, frame pacing, and extensive lifetime conformance coverage.\n\nThe seven-destination connected route now cuts peak working/private memory roughly in half, returns Caul to 125-153 FPS locally, and produces no WER or AMD reset.\n\nCo-authored-by: OpenAI Codex <codex@openai.com>

src/AcDream.App/UI/UiRoot.cs

@@ -197,7 +197,7 @@ public sealed class UiRoot : UiElement
         // A listener may synchronously close/remove a window. Snapshot the walk,
         // then skip children no longer owned by this parent so a deleted subtree
         // cannot receive a stale pulse and collection mutation cannot invalidate it.
-        foreach (var child in element.Children.ToArray())
+        foreach (var child in element.ChildrenBackToFrontSnapshot())
             if (ReferenceEquals(child.Parent, element))
                 BroadcastGlobalUiTime(child, nowSeconds);
     }
@@ -898,10 +898,7 @@ public sealed class UiRoot : UiElement
         }
 
         // Walk top-level children in reverse Z-order (topmost first).
-        var kids = new UiElement[Children.Count];
-        for (int i = 0; i < Children.Count; i++) kids[i] = Children[i];
-        Array.Sort(kids, static (a, b) => b.ZOrder.CompareTo(a.ZOrder));
-        foreach (var c in kids)
+        foreach (var c in ChildrenFrontToBackSnapshot())
         {
             var cp = c.ScreenPosition;
             var hit = c.HitTest(x - cp.X, y - cp.Y);