Camo: generalize brightness + add persistent saturation

Move brightness out of the half-lambert diffuse term to a final exposure
multiply on the whole shaded body color (diffuse + GI + specular), and add
a saturation grade (0 = neutral, -1 = grayscale, >0 = boosted) on the same
final stage. Saturation rides as a 4th component on CamoKnobs (Vector3 ->
Vector4) so it inherits all three persistence paths: HUD JSON, network
replication (_camo NetworkVariable), and painting-slot metadata. Wires the
renamed Slider_Brightness and new Slider_Saturation. Bumps HudFileVersion
and PaintMetaVersion with load-time remaps so existing paintings keep their
look (old 1=neutral saturation remaps to 0=neutral).

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

Assets/Scripts/Components/MeshPainter/MeshPainter.cs

@@ -78,6 +78,16 @@ public partial class MeshPainter : MonoBehaviour
         set => SetMatFloat(SpecularDampenId, value);
     }
 
+    /// <summary>General colour saturation of the shaded body (0 = neutral, -1 = greyscale, &gt;0 = punchier).
+    /// A camo body-tone knob alongside <see cref="CamoHalfLambertBrightness"/>; drives the material's
+    /// <c>_Saturation</c> (offset: shader lerps to grey by 1 + value). Persisted + replicated with the
+    /// other camo knobs (see <see cref="CamoKnobs"/>).</summary>
+    public float CamoSaturation
+    {
+        get => GetMatFloat(SaturationId, 0f);
+        set => SetMatFloat(SaturationId, value);
+    }
+
     // Painted-height look knobs on the same material instance, surfaced/guarded/persisted/replicated
     // like the camo knobs above. Defaults match the shader so the unpainted look is unchanged.
 
@@ -104,11 +114,12 @@ public partial class MeshPainter : MonoBehaviour
         set => SetMatFloat(ParallaxId, Mathf.Max(0f, value) * ParallaxBase);
     }
 
-    /// <summary>The three camo knobs as one vector (x = half-Lambert, y = its brightness, z = specular dampen).</summary>
-    public Vector3 CamoKnobs
+    /// <summary>The four camo knobs as one vector (x = half-Lambert, y = brightness, z = specular dampen,
+    /// w = saturation) - one payload for persistence + network replication.</summary>
+    public Vector4 CamoKnobs
     {
-        get => new(CamoHalfLambert, CamoHalfLambertBrightness, CamoSpecularDampen);
-        set { CamoHalfLambert = value.x; CamoHalfLambertBrightness = value.y; CamoSpecularDampen = value.z; }
+        get => new(CamoHalfLambert, CamoHalfLambertBrightness, CamoSpecularDampen, CamoSaturation);
+        set { CamoHalfLambert = value.x; CamoHalfLambertBrightness = value.y; CamoSpecularDampen = value.z; CamoSaturation = value.w; }
     }
 
     /// <summary>The three painted-height knobs as one vector (x = occlusion threshold, y = relief normal intensity, z = parallax intensity).</summary>
@@ -454,6 +465,7 @@ public partial class MeshPainter : MonoBehaviour
     private const float ParallaxBase = 0.02f;
     private static readonly int HalfLambertId = Shader.PropertyToID("_HalfLambert");
     private static readonly int HalfLambertBrightnessId = Shader.PropertyToID("_HalfLambertBrightness");
+    private static readonly int SaturationId = Shader.PropertyToID("_Saturation");
     private static readonly int SpecularDampenId = Shader.PropertyToID("_SpecularDampen");
     private static readonly int XRayColorId = Shader.PropertyToID("_XRayColor");
     private static readonly int XRayPulseSpeedId = Shader.PropertyToID("_XRayPulseSpeed");