feat(D.2b): LayoutImporter — read layout + resolve inheritance + build tree

Implements Task 5 of the LayoutDesc Importer (Plan 1 — vitals conformance).

Pure layer (BuildFromInfos / Build):
- ImportedLayout result type: UiElement root + O(1) FindElement(uint id) lookup
- BuildWidget dispatches via DatWidgetFactory.Create; skips Type-12 prototypes (null)
- Meters consume their children (DatWidgetFactory already extracted slice ids —
  adding the dat children as UiElement nodes would duplicate geometry)
- All other element types recurse children generically via AddChild

Dat shell (Import):
- Loads LayoutDesc from dats; null-safe if layout is absent
- Resolves each top-level ElementDesc to ElementInfo via Resolve():
  BaseElement/BaseLayoutId chain with (layoutId,elementId) cycle guard
- ToInfo(): reads ElementDesc scalar fields (uint → float cast) + DirectState +
  named States (UIStateId.ToString() as key)
- ReadState(): extracts first MediaDescImage (File + DrawMode) per state +
  font DID from Properties[0x1A] → ArrayBaseProperty → DataIdBaseProperty.Value
- Each sibling element gets a fresh base-chain set (siblings don't share guards)

DRW API: all members confirmed from VitalsLayoutDump.cs usings — no
adjustments needed: LayoutDesc in DBObjs; ElementDesc/StateDesc/MediaDescImage/
ArrayBaseProperty/DataIdBaseProperty in Types; DrawModeType/UIStateId in Enums.

Tests (3/3 green):
- BuildFromInfos_HealthMeter_IsUiMeterAtRect — Type-7 child → UiMeter, Left=5, Width=150
- BuildFromInfos_Type12Child_IsSkipped_Type3Present — prototype absent, container present
- BuildFromInfos_MeterWithChildren_MeterPresent_ChildrenNotInTree — meter findable,
  both dat-children absent, UiMeter.Children empty

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -0,0 +1,105 @@
+using AcDream.App.UI;
+using AcDream.App.UI.Layout;
+
+namespace AcDream.App.Tests.UI.Layout;
+
+/// <summary>
+/// Pure unit tests for <see cref="LayoutImporter.BuildFromInfos"/> — no dats, no GL.
+/// Verifies the tree-builder: widget dispatch, Type-12 skipping, and meter child consumption.
+/// </summary>
+public class LayoutImporterTests
+{
+    private static (uint, int, int) NoTex(uint _) => (0, 0, 0);
+
+    // ── Test 1: Health meter element → UiMeter with correct rect ─────────────
+
+    /// <summary>
+    /// A Type-7 (meter) child element with X=5,Y=5,W=150,H=16 must produce a UiMeter
+    /// that is findable by its id, positioned at Left=5, Width=150.
+    /// The resolve lambda is a 1-arg Func&lt;uint,(uint,int,int)&gt;.
+    /// </summary>
+    [Fact]
+    public void BuildFromInfos_HealthMeter_IsUiMeterAtRect()
+    {
+        var root   = new ElementInfo { Id = 0x100005F9, Type = 3, Width = 160, Height = 58 };
+        var health = new ElementInfo { Id = 0x100000E6, Type = 7, X = 5, Y = 5, Width = 150, Height = 16 };
+
+        var tree = LayoutImporter.BuildFromInfos(root, new[] { health }, NoTex, null);
+
+        var found = tree.FindElement(0x100000E6);
+        Assert.IsType<UiMeter>(found);
+        Assert.Equal(5f,   found!.Left);
+        Assert.Equal(150f, found.Width);
+    }
+
+    // ── Test 2: Type-12 child is skipped; Type-3 sibling is present ──────────
+
+    /// <summary>
+    /// A root with two children: one Type-12 style prototype and one Type-3 container.
+    /// The Type-12 must be absent from the tree (FindElement returns null);
+    /// the Type-3 must be present.
+    /// </summary>
+    [Fact]
+    public void BuildFromInfos_Type12Child_IsSkipped_Type3Present()
+    {
+        var root      = new ElementInfo { Id = 0x10000001, Type = 3, Width = 160, Height = 58 };
+        var prototype = new ElementInfo { Id = 0x20000001, Type = 12, Width = 0, Height = 0 };
+        var container = new ElementInfo { Id = 0x20000002, Type = 3,  Width = 100, Height = 20 };
+
+        var tree = LayoutImporter.BuildFromInfos(root, new[] { prototype, container }, NoTex, null);
+
+        // Type-12 must be absent.
+        Assert.Null(tree.FindElement(0x20000001));
+        // Type-3 must be present.
+        Assert.NotNull(tree.FindElement(0x20000002));
+    }
+
+    // ── Test 3: Meter consumes its children — child ids not in byId ──────────
+
+    /// <summary>
+    /// A meter (Type 7) whose children are the 3-slice back/front containers.
+    /// The meter itself must be findable; its direct children must NOT appear as
+    /// separate nodes in the tree (meters own their children, not the generic tree).
+    /// </summary>
+    [Fact]
+    public void BuildFromInfos_MeterWithChildren_MeterPresent_ChildrenNotInTree()
+    {
+        const uint MeterId      = 0x100000E6u;
+        const uint BackLayerId  = 0x100000E7u;
+        const uint FrontLayerId = 0x00000002u;
+
+        // Build a minimal meter with back + front containers, each with 3 slice children.
+        var backContainer  = BuildSliceContainer(BackLayerId,  ReadOrder: 0,
+            l: 0x0600747Eu, t: 0x0600747Fu, r: 0x06007480u);
+        var frontContainer = BuildSliceContainer(FrontLayerId, ReadOrder: 1,
+            l: 0x06007481u, t: 0x06007482u, r: 0x06007483u);
+
+        var meter = new ElementInfo { Id = MeterId, Type = 7, Width = 150, Height = 16 };
+        meter.Children.Add(backContainer);
+        meter.Children.Add(frontContainer);
+
+        var root = new ElementInfo { Id = 0x100005F9, Type = 3, Width = 160, Height = 58 };
+
+        var tree = LayoutImporter.BuildFromInfos(root, new[] { meter }, NoTex, null);
+
+        // The meter widget is present.
+        Assert.IsType<UiMeter>(tree.FindElement(MeterId));
+        // The meter's dat-children are NOT separate UiElement nodes.
+        Assert.Null(tree.FindElement(BackLayerId));
+        Assert.Null(tree.FindElement(FrontLayerId));
+        // The UiMeter itself has no Ui children (meters consume their children internally).
+        var uiMeter = (UiMeter)tree.FindElement(MeterId)!;
+        Assert.Empty(uiMeter.Children);
+    }
+
+    // ── Helpers ───────────────────────────────────────────────────────────────
+
+    private static ElementInfo BuildSliceContainer(uint id, uint ReadOrder, uint l, uint t, uint r)
+    {
+        var c = new ElementInfo { Id = id, Type = 3, ReadOrder = ReadOrder };
+        c.Children.Add(new ElementInfo { X = 0,   StateMedia = { [""] = (l, 1) } });
+        c.Children.Add(new ElementInfo { X = 10,  StateMedia = { [""] = (t, 1) } });
+        c.Children.Add(new ElementInfo { X = 140, StateMedia = { [""] = (r, 1) } });
+        return c;
+    }
+}