UITK HUD rework + build palette (click-to-place ghost)

Rebuild the in-game HUD on UI Toolkit (HudUi/HudSystem, Aether palette) consistent with the menu; build-palette bar (BuildPaletteState) drives cursor->cell ground-ghost preview (green/red via BuildPreviewMath), left-click place / right-click cancel / rotate; fire suppressed in build mode; combat juice restyle. +4 BuildPreviewMath EditMode tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/_Project/Tests/EditMode/BuildPreviewMathTests.cs

@@ -0,0 +1,55 @@
+using NUnit.Framework;
+using ProjectM.Simulation;
+using Unity.Mathematics;
+
+namespace ProjectM.Tests
+{
+    /// <summary>
+    /// Pure tests for <see cref="BuildPreviewMath"/> — the client build-ghost validity (in-plot, unoccupied,
+    /// affordable) that mirrors the server's authoritative BuildPlaceSystem check, colouring the ground ghost
+    /// green (valid) vs red (the first failing reason).
+    /// </summary>
+    public class BuildPreviewMathTests
+    {
+        static BaseAnchor Anchor() => new BaseAnchor
+        {
+            AnchorPos = new float3(0, 0, 0),
+            GridOrigin = new float3(0, 0, 0),
+            CellSize = 1f,
+            GridDims = new int2(8, 8),
+        };
+
+        [Test]
+        public void InPlot_Unoccupied_Affordable_IsValid()
+        {
+            Assert.AreEqual(BuildPreviewMath.Valid,
+                BuildPreviewMath.Evaluate(Anchor(), new int2(3, 3), occupied: false, have: 50, cost: 20));
+        }
+
+        [Test]
+        public void OutOfPlot_Reported_First()
+        {
+            Assert.AreEqual(BuildPreviewMath.OutOfPlot,
+                BuildPreviewMath.Evaluate(Anchor(), new int2(99, 0), occupied: true, have: 0, cost: 999),
+                "Out-of-plot is reported before occupancy / cost.");
+            Assert.AreEqual(BuildPreviewMath.OutOfPlot,
+                BuildPreviewMath.Evaluate(Anchor(), new int2(-1, 3), occupied: false, have: 50, cost: 10));
+        }
+
+        [Test]
+        public void Occupied_Cell_IsBlocked()
+        {
+            Assert.AreEqual(BuildPreviewMath.Occupied,
+                BuildPreviewMath.Evaluate(Anchor(), new int2(3, 3), occupied: true, have: 50, cost: 10));
+        }
+
+        [Test]
+        public void Unaffordable_When_Have_Below_Cost_Exact_Funds_Ok()
+        {
+            Assert.AreEqual(BuildPreviewMath.Unaffordable,
+                BuildPreviewMath.Evaluate(Anchor(), new int2(3, 3), occupied: false, have: 5, cost: 20));
+            Assert.AreEqual(BuildPreviewMath.Valid,
+                BuildPreviewMath.Evaluate(Anchor(), new int2(3, 3), occupied: false, have: 20, cost: 20));
+        }
+    }
+}

Assets/_Project/Tests/EditMode/BuildPreviewMathTests.cs.meta

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+fileFormatVersion: 2
+guid: 2d3f16d92d3045044a9efd5545320111