fix: address code review comments - spelling, doc clarity, halfRow consistency

Agent-Logs-Url: https://github.com/jongalloway/DiagramForge/sessions/105be76e-e00b-4f8a-ae9d-01ea5b8ccb4e

Co-authored-by: jongalloway <68539+jongalloway@users.noreply.github.com>

Author: Copilot

src/DiagramForge/Layout/DefaultLayoutEngine.Sequence.cs

@@ -115,6 +115,7 @@ private static void LayoutSequenceDiagram(
             int startIdx = Convert.ToInt32(startIdxObj, System.Globalization.CultureInfo.InvariantCulture);
             int endIdx   = Convert.ToInt32(endIdxObj,   System.Globalization.CultureInfo.InvariantCulture);
 
+            double halfRow    = messageRowHeight / 2;
             double bandTop    = double.MaxValue;
             double bandBottom = double.MinValue;
 
@@ -134,14 +135,13 @@ private static void LayoutSequenceDiagram(
                 if (y < bandTop)    bandTop    = y;
                 // Use y + rowH - halfRow so consecutive bands meet at a shared
                 // midpoint rather than overlapping.
-                double rowBottom = y + rowH - messageRowHeight / 2;
+                double rowBottom = y + rowH - halfRow;
                 if (rowBottom > bandBottom) bandBottom = rowBottom;
             }
 
             if (bandTop == double.MaxValue)
                 continue; // no enclosed messages found
 
-            double halfRow = messageRowHeight / 2;
             group.X      = 0;
             group.Y      = bandTop    - halfRow;
             group.Width  = canvasWidth;

src/DiagramForge/Parsers/Mermaid/MermaidSequenceParser.cs

@@ -150,6 +150,8 @@ Node GetOrCreateParticipant(string id)
     /// Validates and normalises a rect color specification of the form
     /// <c>rgb(R,G,B)</c> or <c>rgba(R,G,B,A)</c>.
     /// Returns <see langword="false"/> when the input does not match either form.
+    /// Only the structural prefix (<c>rgb(</c> / <c>rgba(</c>) and closing
+    /// parenthesis are validated; individual component values are passed through as-is.
     /// </summary>
     private static bool TryParseRectColor(string colorSpec, out string normalizedColor)
     {

src/DiagramForge/Rendering/SvgStructureWriter.cs

@@ -553,7 +553,7 @@ private static void AppendSequenceRectBand(StringBuilder sb, Group group)
 
         // For rgb() (no embedded alpha) add a fill-opacity so the band is
         // semi-transparent.  For rgba() the caller-supplied alpha takes effect
-        // automatically via the browser's CSS colour parsing.
+        // automatically via the browser's CSS color parsing.
         bool hasEmbeddedAlpha = colorSpec.StartsWith("rgba(", StringComparison.OrdinalIgnoreCase);
         string opacityAttr = hasEmbeddedAlpha ? string.Empty : " fill-opacity=\"0.2\"";