Initial commit: Unity mesh painter project

Unity 6000.3 (URP) project with live mesh painting in play mode.

- MeshPainter.cs: paint a SkinnedMesh with the mouse, seamless across
  UV islands via 3D-space painting, GPU and CPU backends (switchable),
  edge-padding/dilation against bilinear seam bleed
- FrameRateLimiter.cs: simple frame rate limiting component
- MeshPaintBrush / MeshPaintDilate shaders for the GPU paint path
- Unity-specific .gitignore and .gitattributes

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

ProjectSettings/NavMeshAreas.asset

@@ -0,0 +1,91 @@
+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!126 &1
+NavMeshProjectSettings:
+  m_ObjectHideFlags: 0
+  serializedVersion: 2
+  areas:
+  - name: Walkable
+    cost: 1
+  - name: Not Walkable
+    cost: 1
+  - name: Jump
+    cost: 2
+  - name: 
+    cost: 1
+  - name: 
+    cost: 1
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+    cost: 1
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+  - name: 
+    cost: 1
+  - name: 
+    cost: 1
+  m_LastAgentTypeID: -887442657
+  m_Settings:
+  - serializedVersion: 2
+    agentTypeID: 0
+    agentRadius: 0.5
+    agentHeight: 2
+    agentSlope: 45
+    agentClimb: 0.75
+    ledgeDropHeight: 0
+    maxJumpAcrossDistance: 0
+    minRegionArea: 2
+    manualCellSize: 0
+    cellSize: 0.16666667
+    manualTileSize: 0
+    tileSize: 256
+    accuratePlacement: 0
+    debug:
+      m_Flags: 0
+  m_SettingNames:
+  - Humanoid