fix: correctly align HEAD on absolute left and fix empty column gap

1. 修复了 offsetX 预留逻辑：之前在循环外预留会导致所有路径被强行向右推一列。现在改为在循环内动态判断，Slot 0 (X=10) 严格为 HEAD 路径预留。
2. 修复了“空列”视觉 BUG：不再强行在 maxOffsetOld 中包含预留位，确保 commit 消息的边距计算紧凑。
3. 移除了 cherry-pick 过程中意外引入的 IsHoveredRelated 和 DotType.Filter 改动。
4. 确保 HEAD 路径始终占据视觉上的第一列，且其他并行分支在 HEAD 之前出现时会正确跳过第一列，不留视觉空隙。

FAILED test cases: NONE

Author: heartacker

src/Models/CommitGraph.cs

@@ -108,26 +108,23 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                     unsolved.Insert(0, headPath);
                 }
 
-                // 2. Reserve leftmost column (offsetX) for HEAD path if not yet found
-                var offsetX = 4 - halfWidth;
-                if (alwaysShowCurrentHeadOnLeft && headPath == null && headPathSHAs.Count > 0)
-                    offsetX += unitWidth;
-
-                // 3. Keep track of max offsetX used in previous rows for margin calculation
+                // 2. Keep track of max offsetX used in previous rows for margin calculation
                 var maxOffsetOld = 0.0;
                 foreach (var l in unsolved)
                     maxOffsetOld = Math.Max(maxOffsetOld, l.LastX);
-                if (unsolved.Count == 0)
-                    maxOffsetOld = offsetX + unitWidth;
 
-                // 4. Process existing paths
+                // 3. Process existing paths
+                var offsetX = 4 - halfWidth;
                 foreach (var l in unsolved)
                 {
+                    offsetX += unitWidth;
+                    if (alwaysShowCurrentHeadOnLeft && headPathSHAs.Count > 0 && l != headPath && offsetX == 4 - halfWidth + unitWidth)
+                        offsetX += unitWidth;
+
                     if (l.Next.Equals(commit.SHA, StringComparison.Ordinal))
                     {
                         if (major == null)
                         {
-                            offsetX += unitWidth;
                             major = l;
 
                             if (commit.Parents.Count > 0)
@@ -151,7 +148,6 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                     }
                     else
                     {
-                        offsetX += unitWidth;
                         l.Pass(offsetX, offsetY, halfHeight);
                     }
                 }
@@ -164,7 +160,7 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                 }
                 ended.Clear();
 
-                // 5. Create new curve for branch tip or new merged commit
+                // 4. Create new curve for branch tip or new merged commit
                 if (major == null)
                 {
                     // If this is the start of the HEAD lineage, place it in the reserved column (index 0)
@@ -182,6 +178,9 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                     else if (commit.Parents.Count > 0)
                     {
                         offsetX += unitWidth;
+                        if (alwaysShowCurrentHeadOnLeft && headPathSHAs.Count > 0 && offsetX == 4 - halfWidth + unitWidth)
+                            offsetX += unitWidth;
+
                         major = new PathHelper(commit.Parents[0], isMerged, colorPicker.Next(), new Point(offsetX, offsetY));
                         unsolved.Add(major);
                         temp.Paths.Add(major.Path);
@@ -233,6 +232,8 @@ public static CommitGraph Parse(List<Commit> commits, bool firstParentOnlyEnable
                         else
                         {
                             offsetX += unitWidth;
+                            if (alwaysShowCurrentHeadOnLeft && headPathSHAs.Count > 0 && offsetX == 4 - halfWidth + unitWidth)
+                                offsetX += unitWidth;
 
                             // Create new curve for parent commit that not includes before
                             var l = new PathHelper(parentHash, isMerged, colorPicker.Next(), position, new Point(offsetX, position.Y + halfHeight));