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/XRSettings.asset

@@ -0,0 +1,10 @@
+{
+    "m_SettingKeys": [
+        "VR Device Disabled",
+        "VR Device User Alert"
+    ],
+    "m_SettingValues": [
+        "False",
+        "False"
+    ]
+}