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/UiDatElementTests.cs

@@ -33,4 +33,58 @@ public class UiDatElementTests
         var e = new UiDatElement(info, _ => (0, 0, 0)) { ActiveState = "NoSuchState" };
         Assert.Equal(0x06000005u, e.ActiveMedia().File);
     }
+
+    // ── G1 tests: DefaultStateName + "Normal" implicit default ───────────────
+
+    /// <summary>
+    /// Task G1 change 5: when an element has no DefaultStateName but does have a "Normal"
+    /// state sprite, the ctor should default ActiveState to "Normal" so the element
+    /// renders its normal-state sprite without requiring explicit state assignment.
+    /// </summary>
+    [Fact]
+    public void UiDatElement_DefaultsActiveStateToNormal_WhenNormalPresent()
+    {
+        var info = new ElementInfo();
+        info.StateMedia["Normal"] = (0x0000AAAAu, 1);
+        info.StateMedia["Hover"]  = (0x0000BBBBu, 1);
+
+        var e = new UiDatElement(info, _ => (0, 0, 0));
+
+        // Should have defaulted to "Normal" state.
+        Assert.Equal(0x0000AAAAu, e.ActiveMedia().File);
+    }
+
+    /// <summary>
+    /// Task G1 change 5: when DefaultStateName is set (e.g. "Minimized"),
+    /// it takes priority over the "Normal" implicit default.
+    /// </summary>
+    [Fact]
+    public void UiDatElement_DefaultsActiveStateToDefaultStateName_WhenSet()
+    {
+        var info = new ElementInfo { DefaultStateName = "Minimized" };
+        info.StateMedia["Minimized"] = (0x0000BBBBu, 1);
+        info.StateMedia["Maximized"] = (0x0000CCCCu, 1);
+        info.StateMedia["Normal"]    = (0x0000DDDDu, 1);
+
+        var e = new UiDatElement(info, _ => (0, 0, 0));
+
+        // DefaultStateName "Minimized" wins over "Normal" implicit default.
+        Assert.Equal(0x0000BBBBu, e.ActiveMedia().File);
+    }
+
+    /// <summary>
+    /// Task G1 change 5: elements with only a DirectState sprite and no "Normal" state
+    /// should still default to "" (DirectState) — no regression for chrome/grip elements.
+    /// </summary>
+    [Fact]
+    public void UiDatElement_NoDefaultStateName_NoNormal_DefaultsToDirectState()
+    {
+        var info = new ElementInfo();
+        info.StateMedia[""] = (0x06007777u, 1);  // DirectState only (e.g. vitals chrome corner)
+
+        var e = new UiDatElement(info, _ => (0, 0, 0));
+
+        // No DefaultStateName, no "Normal" state → ActiveState stays "" (DirectState).
+        Assert.Equal(0x06007777u, e.ActiveMedia().File);
+    }
 }