test(D.2b): vitals importer conformance — golden fixture + tree/slice/chrome checks

Job 1: extract LayoutImporter.ImportInfos() (public dat-shell half that returns the
resolved ElementInfo tree without building widgets) so fixture generation and
conformance tests can call it directly. Import() now delegates to ImportInfos() +
Build() — existing 32 Layout tests stay green.

Job 2: generate tests/AcDream.App.Tests/UI/Layout/fixtures/vitals_2100006C.json
from the real portal.dat via a throwaway [Fact] generator (deleted, not committed).
System.Text.Json with IncludeFields=true — ValueTuple serializes as Item1/Item2.
Pre-write validation confirmed health meter BackLeft=0x0600747E FrontRight=0x06007483
rect (5,5,150,16). Round-trip deserialization re-validated before writing.

Job 3: FixtureLoader.LoadVitals() deserializes the fixture from the test output
directory (CopyToOutputDirectory item in csproj) and returns ImportedLayout via
LayoutImporter.Build(root, _ => (0,0,0), null) — no dats, no GL.

Job 4: LayoutConformanceTests — 3 golden tests (35 asserts total):
  - VitalsTree_HasThreeMetersAtExpectedRects: 3 meters at x=5, w=150, h=16, y=5/21/37
  - VitalsTree_MetersHaveExpectedSliceIds: all 18 back+front slice ids health/stamina/mana
  - VitalsTree_ChromeCornerHasExpectedSprite: TL corner 0x10000633 → sprite 0x060074C3

Full App suite: 326 pass / 1 skip (pre-existing) / 0 fail. Build: 0 errors, 0 warnings.
Throwaway generator not committed (confirmed via git status).

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

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

@@ -0,0 +1,38 @@
+using System.IO;
+using System.Text.Json;
+using AcDream.App.UI.Layout;
+
+namespace AcDream.App.Tests.UI.Layout;
+
+/// <summary>
+/// Loads the committed vitals ElementInfo fixture and builds the widget tree —
+/// no dats required. The fixture was generated from layout <c>0x2100006C</c>
+/// via the real portal.dat and serialized with <see cref="System.Text.Json"/>.
+/// </summary>
+public static class FixtureLoader
+{
+    private static readonly JsonSerializerOptions _opts = new()
+    {
+        IncludeFields = true,
+    };
+
+    /// <summary>
+    /// Deserializes the committed <c>vitals_2100006C.json</c> fixture (copied to
+    /// the test output directory via the csproj <c>CopyToOutputDirectory</c> item)
+    /// into an <see cref="ElementInfo"/> tree, then builds and returns the
+    /// <see cref="ImportedLayout"/> using a null-returning sprite resolver and no
+    /// dat font — sufficient for conformance checks on tree structure and slice ids.
+    /// </summary>
+    public static ImportedLayout LoadVitals()
+    {
+        var fixturePath = Path.Combine(AppContext.BaseDirectory, "UI", "Layout", "fixtures", "vitals_2100006C.json");
+        if (!File.Exists(fixturePath))
+            throw new FileNotFoundException($"Vitals fixture not found at: {fixturePath}");
+
+        var json = File.ReadAllText(fixturePath, System.Text.Encoding.UTF8);
+        var root = JsonSerializer.Deserialize<ElementInfo>(json, _opts)
+            ?? throw new InvalidOperationException("Failed to deserialize vitals fixture.");
+
+        return LayoutImporter.Build(root, _ => (0u, 0, 0), null);
+    }
+}