feat(studio): dump LayoutSource — preview any retail window from the UI dump

Adds Task 4b: a second load path for the UI Studio that reads the committed
retail UI layout dump (docs/research/2026-06-25-retail-ui-layout-dump.json)
and renders any of the 26 retail windows as a static sprite hierarchy.

New files:
- src/AcDream.App/Studio/UiDumpModel.cs — POCOs + System.Text.Json parse of
  the dump (UiDump, DumpPanel, DumpNode, DumpRect, DumpStateSet, DumpImage,
  DumpState + UiDumpModel static helpers: Parse, ListSlugs, PickImageId).
- src/AcDream.App/Studio/DumpLayout.cs — DumpLayout.Load(path, slug, resolve,
  out err): parses the dump, finds the panel by slug, builds a UiElement tree.
  Internal DumpSpriteElement draws its sprite via DrawSprite (not reusing
  UiDatElement — avoids the ElementInfo/StateMedia dat-import dependency for
  this static mockup). DumpGroupElement is a transparent container for Group
  nodes. Rect basis is ABSOLUTE in the dump (verified: inventory root at
  absolute x=500 and its children also start at x≈500 — child offset from
  parent is 0–50px, not 500px); DumpLayout subtracts parent rect to produce
  parent-relative Left/Top for each child.
- tests/AcDream.App.Tests/Studio/DumpLayoutTests.cs — 5 tests covering:
  inventory load with 0x100001D5 check + >= 40 nodes, unknown slug → null+err,
  root at origin, children are parent-relative, all 26 slugs smoke-load.

Modified files:
- StudioOptions: adds DumpSlug + DumpFile fields; --dump <slug> and
  --dump-file <path> args; ResolveDumpFile() walks up to the solution root
  to find the default dump JSON (mirrors ConformanceDats.SolutionRoot()).
  --dump suppresses the default vitals layout so the two modes are exclusive.
- StudioWindow.OnLoad: when DumpSlug is set, loads via DumpLayout (no
  FixtureProvider, no controllers — static structure only); else falls
  through to the existing LayoutSource + FixtureProvider path.

Results: DumpLayoutTests 5/5 passed; full AcDream.App.Tests 609 passed, 2
skipped (same as before); dotnet build green, 0 warnings.

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

src/AcDream.App/Studio/UiDumpModel.cs

@@ -0,0 +1,198 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace AcDream.App.Studio;
+
+// ─────────────────────────────────────────────────────────────────────────────
+// UiDumpModel — POCOs for docs/research/2026-06-25-retail-ui-layout-dump.json
+//
+// Schema (v1):
+//   { "version":1, "panels":[ { "id":int, "slug":string, "title":string,
+//       "bucket":string, "parent_slug":string|null,
+//       "width":int, "height":int,
+//       "nodes":[ { "traversal_index":int, "element_id":int,
+//                   "layout_id":int, "parent_layout_id":int|null,
+//                   "parent_traversal_index":int|null, "base_layout_id":int,
+//                   "rect":{x,y,width,height},
+//                   "widget_kind":"Group"|"Sprite"|"Button"|"Scrollbar"|"Slider",
+//                   "state_set":{ "default_image":{image_id,alpha_image_id}|null,
+//                                 "states":[{state_id,image:{...}}] }
+//               } ] } ] }
+//
+// All ids in the dump are DECIMAL ints (e.g. element_id=268435925 = 0x100001D5,
+// image_id=100693194 = 0x060074CA). Cast to uint before use in dat/GL APIs.
+//
+// Rect coordinates are ABSOLUTE (screen-space origin = panel's design position
+// in retail layout, NOT relative to the parent). DumpLayout.Load converts them
+// to parent-relative when building the UiElement tree.
+// ─────────────────────────────────────────────────────────────────────────────
+
+/// <summary>Top-level container for the retail UI layout dump.</summary>
+public sealed class UiDump
+{
+    [JsonPropertyName("version")]
+    public int Version { get; set; }
+
+    [JsonPropertyName("panels")]
+    public List<DumpPanel> Panels { get; set; } = new();
+}
+
+/// <summary>One panel (window) exported from the retail UI.</summary>
+public sealed class DumpPanel
+{
+    [JsonPropertyName("id")]
+    public long Id { get; set; }
+
+    [JsonPropertyName("slug")]
+    public string Slug { get; set; } = "";
+
+    [JsonPropertyName("title")]
+    public string Title { get; set; } = "";
+
+    [JsonPropertyName("bucket")]
+    public string Bucket { get; set; } = "";
+
+    [JsonPropertyName("parent_slug")]
+    public string? ParentSlug { get; set; }
+
+    [JsonPropertyName("width")]
+    public float Width { get; set; }
+
+    [JsonPropertyName("height")]
+    public float Height { get; set; }
+
+    [JsonPropertyName("nodes")]
+    public List<DumpNode> Nodes { get; set; } = new();
+}
+
+/// <summary>One element node within a panel's traversal list.</summary>
+public sealed class DumpNode
+{
+    [JsonPropertyName("traversal_index")]
+    public int TraversalIndex { get; set; }
+
+    [JsonPropertyName("element_id")]
+    public long ElementId { get; set; }
+
+    [JsonPropertyName("layout_id")]
+    public long LayoutId { get; set; }
+
+    [JsonPropertyName("parent_layout_id")]
+    public long? ParentLayoutId { get; set; }
+
+    [JsonPropertyName("parent_traversal_index")]
+    public int? ParentTraversalIndex { get; set; }
+
+    [JsonPropertyName("base_layout_id")]
+    public long BaseLayoutId { get; set; }
+
+    [JsonPropertyName("rect")]
+    public DumpRect Rect { get; set; } = new();
+
+    [JsonPropertyName("widget_kind")]
+    public string WidgetKind { get; set; } = "Group";
+
+    [JsonPropertyName("state_set")]
+    public DumpStateSet StateSet { get; set; } = new();
+}
+
+/// <summary>Absolute screen-space rect (see comment above — must subtract parent rect for UiElement).</summary>
+public sealed class DumpRect
+{
+    [JsonPropertyName("x")]
+    public float X { get; set; }
+
+    [JsonPropertyName("y")]
+    public float Y { get; set; }
+
+    [JsonPropertyName("width")]
+    public float Width { get; set; }
+
+    [JsonPropertyName("height")]
+    public float Height { get; set; }
+}
+
+/// <summary>State set for a node — default image plus per-state overrides.</summary>
+public sealed class DumpStateSet
+{
+    [JsonPropertyName("default_image")]
+    public DumpImage? DefaultImage { get; set; }
+
+    [JsonPropertyName("states")]
+    public List<DumpState> States { get; set; } = new();
+}
+
+/// <summary>Image reference (RenderSurface dat id + optional separate alpha surface).</summary>
+public sealed class DumpImage
+{
+    [JsonPropertyName("image_id")]
+    public long ImageId { get; set; }
+
+    [JsonPropertyName("alpha_image_id")]
+    public long? AlphaImageId { get; set; }
+}
+
+/// <summary>A named state override.</summary>
+public sealed class DumpState
+{
+    [JsonPropertyName("state_id")]
+    public int StateId { get; set; }
+
+    [JsonPropertyName("image")]
+    public DumpImage Image { get; set; } = new();
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Helper statics
+// ─────────────────────────────────────────────────────────────────────────────
+
+/// <summary>
+/// Parsing helpers for the retail UI dump JSON.
+/// </summary>
+public static class UiDumpModel
+{
+    private static readonly JsonSerializerOptions _opts = new()
+    {
+        PropertyNameCaseInsensitive = true,
+        AllowTrailingCommas         = true,
+        ReadCommentHandling         = JsonCommentHandling.Skip,
+    };
+
+    /// <summary>Parse the full dump from a file path. Returns null on failure.</summary>
+    public static UiDump? Parse(string path)
+    {
+        try
+        {
+            using var stream = File.OpenRead(path);
+            return JsonSerializer.Deserialize<UiDump>(stream, _opts);
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    /// <summary>
+    /// Return the list of slugs in the dump (for smoke-testing every panel).
+    /// Returns an empty list if the file cannot be parsed.
+    /// </summary>
+    public static IReadOnlyList<string> ListSlugs(string path)
+    {
+        var dump = Parse(path);
+        if (dump is null) return Array.Empty<string>();
+        return dump.Panels.Select(p => p.Slug).ToList();
+    }
+
+    /// <summary>
+    /// Pick the sprite id to use for a node: prefer default_image.image_id;
+    /// fall back to states[0].image.image_id; return 0 if neither exists.
+    /// </summary>
+    public static uint PickImageId(DumpNode node)
+    {
+        if (node.StateSet.DefaultImage is { ImageId: > 0 } di)
+            return (uint)di.ImageId;
+        if (node.StateSet.States.Count > 0 && node.StateSet.States[0].Image.ImageId > 0)
+            return (uint)node.StateSet.States[0].Image.ImageId;
+        return 0u;
+    }
+}