fix: wide char bugs in table truncation, column resize, and overlay flash

Table rendering: truncating a wide character at a column boundary now
replaces it with a space instead of dropping the continuation cell and
corrupting all subsequent columns.

Table column resize: fixed-width columns are no longer proportionally
shrunk when the table narrows — only auto-width columns absorb the
deficit. Fixed columns shrink only as a last resort.

Overlay flash/fade: add SetCellColors to CharacterBuffer for color-only
updates that skip CleanupWideCharAt, preventing wide character pairs
from being destroyed during overlay animation passes.

Author: nickprotop

SharpConsoleUI/Helpers/ColorBlendHelper.cs

@@ -52,12 +52,9 @@ public static void ApplyColorOverlay(
 				var newBg = BlendColor(cell.Background, overlayColor, intensity);
 				var newFg = BlendColor(cell.Foreground, overlayColor, intensity * foregroundBlendRatio);
 
-				var updated = new Layout.Cell(cell.Character, newFg, newBg, cell.Decorations)
-				{
-					IsWideContinuation = cell.IsWideContinuation,
-					Combiners = cell.Combiners
-				};
-				buffer.SetCell(x, y, updated);
+				// Use color-only update to avoid CleanupWideCharAt destroying
+				// wide character pairs (emoji, CJK) during overlay passes
+				buffer.SetCellColors(x, y, newFg, newBg);
 			}
 		}
 	}

SharpConsoleUI/Layout/CharacterBuffer.cs

@@ -265,6 +265,27 @@ public void SetCell(int x, int y, Cell cell)
 			}
 		}
 
+		/// <summary>
+		/// Updates only the foreground and background colors of a cell without modifying
+		/// the character, decorations, wide-char flags, or combiners.
+		/// Does not trigger wide-character cleanup — safe for overlay effects (flash, fade)
+		/// that blend colors without changing cell content.
+		/// </summary>
+		public void SetCellColors(int x, int y, Color foreground, Color background)
+		{
+			if (x < 0 || x >= Width || y < 0 || y >= Height)
+				return;
+
+			ref var existing = ref _cells[x, y];
+			if (!existing.Foreground.Equals(foreground) || !existing.Background.Equals(background))
+			{
+				existing.Foreground = foreground;
+				existing.Background = background;
+				existing.Dirty = true;
+				ExpandDirtyRegion(x, y);
+			}
+		}
+
 		/// <summary>
 		/// Writes a string at the specified position with the given colors.
 		/// Wide characters occupy 2 columns with a continuation cell for the right half.