feat(ui): port retail selected-item mana

Parse and route the complete 0x0264 guid/fraction/valid response, send exact 0x0263 item-mana queries, and reproduce retail meter visibility plus guid-zero cancellation for mana and health selection changes. Keep the behavior in Core state and the retained selected-object controller with wire/state/UI conformance coverage.

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

tests/AcDream.Core.Tests/Items/ItemManaStateTests.cs

@@ -0,0 +1,33 @@
+using AcDream.Core.Items;
+using Xunit;
+
+namespace AcDream.Core.Tests.Items;
+
+public sealed class ItemManaStateTests
+{
+    [Fact]
+    public void ValidResponseCachesAndRaisesEvent()
+    {
+        var state = new ItemManaState();
+        (uint Guid, float Percent, bool Valid)? observed = null;
+        state.ItemManaChanged += (guid, percent, valid) => observed = (guid, percent, valid);
+
+        state.OnQueryItemManaResponse(0x50000A01u, 0.75f, valid: true);
+
+        Assert.Equal((0x50000A01u, 0.75f, true), observed);
+        Assert.True(state.HasMana(0x50000A01u));
+        Assert.Equal(0.75f, state.GetManaPercent(0x50000A01u));
+    }
+
+    [Fact]
+    public void InvalidResponseClearsCachedValueAndRaisesEvent()
+    {
+        var state = new ItemManaState();
+        state.OnQueryItemManaResponse(0x50000A01u, 0.75f, valid: true);
+
+        state.OnQueryItemManaResponse(0x50000A01u, 0f, valid: false);
+
+        Assert.False(state.HasMana(0x50000A01u));
+        Assert.Equal(0f, state.GetManaPercent(0x50000A01u));
+    }
+}