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/EditorBuildSettings.asset

@@ -0,0 +1,13 @@
+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!1045 &1
+EditorBuildSettings:
+  m_ObjectHideFlags: 0
+  serializedVersion: 2
+  m_Scenes:
+  - enabled: 1
+    path: Assets/Scenes/SampleScene.unity
+    guid: 99c9720ab356a0642a771bea13969a05
+  m_configObjects:
+    com.unity.input.settings.actions: {fileID: -944628639613478452, guid: 052faaac586de48259a63d0c4782560b, type: 3}
+  m_UseUCBPForAssetBundles: 0