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>

Assets/Shaders/MeshPaintDilate.shader

@@ -0,0 +1,72 @@
+// GPU edge padding / texture dilation against visible UV seams.
+//
+// Between the UV islands there is an unpainted border (gutter). During bilinear
+// sampling at an island edge, the GPU mixes the painted edge with the unpainted
+// base color -> bright seam lines. This pass "bleeds" the painted color up to
+// _Pad texels beyond the island edges.
+//
+// The dilation source is exclusively painted texels (alpha >= 0.5). The padding
+// texels produced get alpha = 0 -> next frame they are NO LONGER a source, so the
+// padding does not grow unbounded (it stays at _Pad texels).
+Shader "Hidden/MeshPaintDilate"
+{
+    Properties
+    {
+        _MainTex ("Texture", 2D) = "white" {}
+    }
+    SubShader
+    {
+        Tags { "RenderType" = "Opaque" }
+        Pass
+        {
+            ZTest Always
+            ZWrite Off
+            Cull Off
+            Blend Off
+
+            CGPROGRAM
+            #pragma vertex vert_img
+            #pragma fragment frag
+            #include "UnityCG.cginc"
+
+            sampler2D _MainTex;
+            float4 _MainTex_TexelSize; // (1/w, 1/h, w, h)
+            int _Pad;
+
+            #define MAXPAD 16
+
+            fixed4 frag (v2f_img i) : SV_Target
+            {
+                fixed4 c = tex2D(_MainTex, i.uv);
+                if (c.a >= 0.5) return c; // already painted -> leave unchanged
+
+                float2 ts = _MainTex_TexelSize.xy;
+                float best = 1e20;
+                fixed3 bestCol = c.rgb;
+                bool found = false;
+
+                // Search the neighborhood (up to _Pad texels) for the nearest painted texel.
+                [loop] for (int y = -MAXPAD; y <= MAXPAD; y++)
+                {
+                    if (abs(y) > _Pad) continue;
+                    [loop] for (int x = -MAXPAD; x <= MAXPAD; x++)
+                    {
+                        if (abs(x) > _Pad) continue;
+                        fixed4 s = tex2D(_MainTex, i.uv + float2(x, y) * ts);
+                        if (s.a >= 0.5)
+                        {
+                            float dd = (float)(x * x + y * y);
+                            if (dd < best) { best = dd; bestCol = s.rgb; found = true; }
+                        }
+                    }
+                }
+
+                // Gutter: color of the nearest painted texel, but alpha = 0 (not a source).
+                if (found) return fixed4(bestCol, 0.0);
+                return c; // out of range -> base color unchanged
+            }
+            ENDCG
+        }
+    }
+    Fallback Off
+}