feat(D.2b): importer renders Type-12-with-sprites + carries DefaultState

Task G1: two gaps blocked chat window static sprite elements from rendering.

Change 1 — DatWidgetFactory: only skip Type-12 elements that have no own
state media (pure style prototypes). A Type-12 element that carries sprites
(e.g. a chat Send button whose derived Type-0 element inherited Type 12 from
its base prototype) now renders as a UiDatElement.

Change 2 — ElementInfo: add DefaultStateName field (string, default "").

Change 3 — LayoutImporter.ToInfo: read ElementDesc.DefaultState.ToString()
into DefaultStateName; normalize Undef/Undefined/0 sentinels to "".

Change 4 — ElementReader.Merge: inherit DefaultStateName (derived wins if
non-empty, else base).

Change 5 — UiDatElement ctor: initialize ActiveState to DefaultStateName
when set; else "Normal" when a Normal-state sprite is present (retail's
implicit default for buttons/tabs); else "" (DirectState). This makes the
Send button, max/min button, and numbered tabs render their default sprite
without requiring explicit state assignment at runtime.

Vitals neutrality: all vitals chrome/grip elements carry DirectState-only
sprites with no "Normal" named state and DefaultStateName="" (Undef in dat),
so their ActiveState stays "" and their existing conformance tests are
unaffected. Vitals text labels (Type 0→12 via Merge, no StateMedia) are
still skipped by the refined Type-12 guard (StateMedia.Count==0).

Tests: 4 new tests (2 in DatWidgetFactoryTests, 3 in UiDatElementTests).
All 386 pass; 387 total (1 pre-existing skip).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/AcDream.App.Tests/UI/Layout/DatWidgetFactoryTests.cs

@@ -71,6 +71,32 @@ public class DatWidgetFactoryTests
         Assert.Equal(7, e!.ZOrder);
     }
 
+    // ── Test G1a: Type 12 with own sprites renders; without sprites is skipped ──
+
+    /// <summary>
+    /// Task G1 change 1: only PURE Type-12 prototypes (no state media) are skipped.
+    /// A Type-12 element that carries its own state media must return a non-null widget.
+    /// </summary>
+    [Fact]
+    public void DatWidgetFactory_Type12WithMedia_Renders()
+    {
+        // Type 12 with a "Normal" state sprite — must render (NOT skipped).
+        var withMedia = new ElementInfo
+        {
+            Type       = 12,
+            Width      = 32,
+            Height     = 16,
+            StateMedia = { ["Normal"] = (0x00001234u, 1) },
+        };
+        var e = DatWidgetFactory.Create(withMedia, NoTex, null);
+        Assert.NotNull(e);
+        Assert.IsType<UiDatElement>(e);
+
+        // Type 12 with NO state media — must still be skipped (pure prototype).
+        var noMedia = new ElementInfo { Type = 12 };
+        Assert.Null(DatWidgetFactory.Create(noMedia, NoTex, null));
+    }
+
     // ── Test 6: Meter slice extraction (the important one) ───────────────────
 
     /// <summary>