feat(selection): port retail polygon picking and vivid marker

Replace the projected Setup-sphere rectangle and independent physics-wall ray with retail's render-coupled picker: only visible server-object parts participate, each exact drawing sphere broad-phases the camera-eye ray, and first-in-DAT-order visual polygon hits globally outrank sphere fallbacks.

Replace the devtools-only procedural triangles with the retained gameplay VividTargetIndicator using retail client-enum surfaces 1..4, radar-blip colorization, Setup selection-sphere framing, and the exact eight-pixel viewport clamp.

Release build succeeds with zero warnings and all 5,886 tests pass with five intentional skips.

Co-authored-by: OpenAI Codex <codex@openai.com>

src/AcDream.App/Rendering/Selection/IRetailSelectionRenderSink.cs

@@ -0,0 +1,17 @@
+using System.Numerics;
+using AcDream.Core.World;
+
+namespace AcDream.App.Rendering.Selection;
+
+/// <summary>
+/// Narrow seam from the normal world draw traversal to retail mouse selection.
+/// Only entities which survive that traversal are published.
+/// </summary>
+internal interface IRetailSelectionRenderSink
+{
+    void AddVisiblePart(
+        WorldEntity entity,
+        int partIndex,
+        uint gfxObjId,
+        Matrix4x4 partWorld);
+}