Drive parallax height and relief from the painted occlusion channel

Reuse the existing occlusion paint channel (no new map, MAP_COUNT stays 3):
0.5 is neutral, above 0.5 raises a hill, below 0.5 sinks a hole and also
fades ambient occlusion (saturate(2*occ)). Bind the MSO map to _ParallaxMap,
enable _PARALLAXMAP, derive a relief normal from the height gradient, and
reseed unpainted occlusion to 0.5 so untouched surfaces stay visually neutral.
Pin the _PARALLAXMAP runtime variant in the build keep-alive material.

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

Assets/Scripts/MeshPainter.cs

@@ -130,9 +130,10 @@ public partial class MeshPainter : MonoBehaviour
     [Range(0f, 1f)]
     public float metallicSmoothnessOpacity = 1f;
 
-    [Tooltip("Ambient occlusion painted into the mask map (1 = fully lit / no darkening, " +
-             "0 = fully occluded / dark). NOTE: URP only darkens INDIRECT light (ambient + " +
-             "reflections), so the effect is subtle under strong direct lighting. 1 = no-op.")]
+    [Tooltip("Occlusion + HEIGHT painted into the mask map (one value, 0..1, 0.5 = neutral/no-op). " +
+             "Drives parallax + a relief normal: 0.5 = flat, >0.5 = raised hill, <0.5 = carved hole. " +
+             "Also drives ambient occlusion, but only the LOWER half darkens: 0.5..1 = fully lit, " +
+             "0.5..0 = AO fades 1..0 (so a hole is also darker). See Custom/PlayerCamoLit.")]
     [Range(0f, 1f)]
     public float occlusion = 0.5f;
 
@@ -284,7 +285,7 @@ public partial class MeshPainter : MonoBehaviour
 
     // Seed colors per map in canonical (material) layout, built once at Start:
     //   albedo   -> RGB color
-    //   MSO      -> R = metallic, G = occlusion (1 = unoccluded), A = smoothness (mask map)
+    //   MSO      -> R = metallic, G = occlusion/height (0.5 = neutral: no relief, AO = 1), A = smoothness
     //   emission -> RGB emission
     private Color32[][] _seedCanonical;
 
@@ -322,6 +323,8 @@ public partial class MeshPainter : MonoBehaviour
     private static readonly int EmissionColorId = Shader.PropertyToID("_EmissionColor");
     private static readonly int OcclusionMapId = Shader.PropertyToID("_OcclusionMap");
     private static readonly int OcclusionStrengthId = Shader.PropertyToID("_OcclusionStrength");
+    private static readonly int ParallaxMapId = Shader.PropertyToID("_ParallaxMap");
+    private static readonly int ParallaxId = Shader.PropertyToID("_Parallax");
     private static readonly int HalfLambertId = Shader.PropertyToID("_HalfLambert");
     private static readonly int HalfLambertBrightnessId = Shader.PropertyToID("_HalfLambertBrightness");
     private static readonly int SpecularDampenId = Shader.PropertyToID("_SpecularDampen");