Refactor Assets/Scripts: trim restating comments, minor structure cleanups

Sweep over 48 files (Editor/ excluded): remove comments that restate the
code, condense class summaries, fix three stale doc statements
(HsvColorPicker alpha bar, PaintHud layoutPrefab, MasterVolume
FallbackDefault). Inline two single-use wrappers (IsPointerOverUi,
BuildModes), drop an unused using, replace a magic literal with the
existing ParallaxBase constant, and convert ~10 UnityEngine.Object null
checks to the implicit-bool convention. No serialized fields, signatures,
RPC/NetworkVariable names, defaults, or #if blocks touched.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Assets/Scripts/Components/MeshPainter/MeshPainter.Net.cs

@@ -73,7 +73,6 @@ public partial class MeshPainter
     /// <summary>True if anyone is listening for replicated stamps (the owner is networked + painting).</summary>
     private bool WantsStampCapture => OnStampCommitted != null;
 
-    /// <summary>Builds the replicated stamp from the current brush state + resolved placement and raises the event.</summary>
     private void EmitStamp(Vector3 p, float r, Vector3 u, Vector3 v, Vector3 n)
     {
         var handler = OnStampCommitted;