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.Persistence.cs

@@ -30,7 +30,8 @@ public partial class MeshPainter
     // is), so saves without a fur.png load fine - the fur map stays seeded (bald). NOTE: the fur.png layout
     // changed to R = length (was RGB colour + A length); pre-change fur.png files load stale length data and
     // should be repainted.
-    private const int PaintMetaVersion = 6;
+    // v8: camoSaturation semantics changed to an offset (0 = neutral, -1 = greyscale; was 1 = neutral in v7).
+    private const int PaintMetaVersion = 8;
 
     private const string MetaFileName = "painting.json";
     private const string AlbedoFileName = "albedo.png";
@@ -57,6 +58,7 @@ public partial class MeshPainter
         public float camoHalfLambert;
         public float camoHalfLambertBrightness;
         public float camoSpecularDampen;
+        public float camoSaturation; // v7+; remapped on load per meta.version (semantics changed in v8)
         public float occlusionThreshold;
         public float heightNormalIntensity;
         public float parallaxIntensity;
@@ -149,6 +151,7 @@ public partial class MeshPainter
                 camoHalfLambert = CamoHalfLambert,
                 camoHalfLambertBrightness = CamoHalfLambertBrightness,
                 camoSpecularDampen = CamoSpecularDampen,
+                camoSaturation = CamoSaturation,
                 occlusionThreshold = OcclusionThreshold,
                 heightNormalIntensity = HeightNormalIntensity,
                 parallaxIntensity = ParallaxIntensity,
@@ -200,6 +203,12 @@ public partial class MeshPainter
             CamoHalfLambert = meta.camoHalfLambert;
             CamoHalfLambertBrightness = meta.camoHalfLambertBrightness;
             CamoSpecularDampen = meta.camoSpecularDampen;
+            // Saturation semantics changed in v8 (0 = neutral, -1 = greyscale; was 1 = neutral in v7).
+            // v7 stored the old scheme -> shift by -1 to preserve its look. Pre-v7 has no field (deserializes
+            // to 0), which is already neutral under the new scheme.
+            CamoSaturation = meta.version >= 8 ? meta.camoSaturation
+                           : meta.version == 7 ? meta.camoSaturation - 1f
+                           : 0f;
             OcclusionThreshold = meta.occlusionThreshold;
             HeightNormalIntensity = meta.heightNormalIntensity;
             ParallaxIntensity = meta.parallaxIntensity;