feat(screenshot): add freehand drawing tool with multi-point path support

- Add freehand tool to AnnotationTool enum
- Extend AnnotationShape with optional points array for multi-point paths
- Implement freehand rendering with smooth line joins and round caps
- Update AnnotationView to collect points during mouse drag for freehand tool
- Add freehand button to toolbar with pencil.tip icon
- Support continuous drawing by appending points during mouseDragged
- Validate freehand shapes require at least 2 points before committing
- Add localization support: Freehand/画笔/畫筆/ペン
- Update toolbar width calculation for 4 tools (rect/circle/arrow/freehand)

Author: qianmoQ

DockMasterPro/Plugins/ScreenshotPlugin/ScreenshotAnnotationModel.swift

@@ -7,6 +7,7 @@ enum AnnotationTool: Equatable {
     case rectangle
     case arrow      // 箭头工具
     case circle     // 圆形/椭圆工具
+    case freehand   // 画笔工具（自由绘制）
 }
 
 // MARK: - Annotation Shape
@@ -17,6 +18,7 @@ struct AnnotationShape {
     var endPoint: NSPoint
     var color: NSColor
     var lineWidth: CGFloat
+    var points: [NSPoint]?    // 用于画笔工具的多点路径
 
     // Shared rendering — draws into whatever NSGraphicsContext is current
     static func render(_ shape: AnnotationShape) {
@@ -104,6 +106,27 @@ struct AnnotationShape {
             shape.color.setFill()
             path.stroke()
             path.fill()
+            
+        case .freehand:
+            // 绘制自由画笔：连接所有点的平滑曲线
+            guard let points = shape.points, points.count >= 2 else { return }
+            
+            let path = NSBezierPath()
+            
+            // 移动到第一个点
+            path.move(to: points[0])
+            
+            // 连接所有点
+            for i in 1..<points.count {
+                path.line(to: points[i])
+            }
+            
+            // 设置样式并绘制
+            path.lineWidth = shape.lineWidth
+            path.lineCapStyle = .round   // 圆角端点，让线条更平滑
+            path.lineJoinStyle = .round  // 圆角连接，让转角更平滑
+            shape.color.setStroke()
+            path.stroke()
         }
     }
 }

DockMasterPro/Plugins/ScreenshotPlugin/ScreenshotAnnotationView.swift

@@ -69,24 +69,53 @@ final class ScreenshotAnnotationView: NSView {
         onDrawingStarted?()
 
         let pt = localPoint(from: event)
-        activeShape = AnnotationShape(
-            tool: tool,
-            startPoint: pt,
-            endPoint: pt,
-            color: session.currentColor,
-            lineWidth: session.currentLineWidth
-        )
+        
+        // 画笔工具需要初始化点数组
+        if tool == .freehand {
+            activeShape = AnnotationShape(
+                tool: tool,
+                startPoint: pt,
+                endPoint: pt,
+                color: session.currentColor,
+                lineWidth: session.currentLineWidth,
+                points: [pt]  // 初始化点数组
+            )
+        } else {
+            activeShape = AnnotationShape(
+                tool: tool,
+                startPoint: pt,
+                endPoint: pt,
+                color: session.currentColor,
+                lineWidth: session.currentLineWidth,
+                points: nil
+            )
+        }
         needsDisplay = true
     }
 
     override func mouseDragged(with event: NSEvent) {
         // 如果没有激活形状，将事件传递给下一个响应者
-        guard activeShape != nil else {
+        guard var shape = activeShape else {
             nextResponder?.mouseDragged(with: event)
             return
         }
 
-        activeShape?.endPoint = localPoint(from: event)
+        let pt = localPoint(from: event)
+        
+        // 画笔工具：添加新点到路径
+        if shape.tool == .freehand {
+            if shape.points == nil {
+                shape.points = [shape.startPoint]
+            }
+            shape.points?.append(pt)
+            shape.endPoint = pt  // 更新终点
+            activeShape = shape
+        } else {
+            // 其他工具：只更新终点
+            shape.endPoint = pt
+            activeShape = shape
+        }
+        
         needsDisplay = true
     }
 
@@ -97,12 +126,34 @@ final class ScreenshotAnnotationView: NSView {
             return
         }
 
-        shape.endPoint = localPoint(from: event)
+        let pt = localPoint(from: event)
+        
+        // 画笔工具：添加最后一个点
+        if shape.tool == .freehand {
+            if shape.points == nil {
+                shape.points = [shape.startPoint]
+            }
+            shape.points?.append(pt)
+            shape.endPoint = pt
+        } else {
+            shape.endPoint = pt
+        }
+        
         activeShape = nil
 
-        let dx = abs(shape.endPoint.x - shape.startPoint.x)
-        let dy = abs(shape.endPoint.y - shape.startPoint.y)
-        if dx > 3 || dy > 3 {
+        // 检查形状是否足够大
+        let isValid: Bool
+        if shape.tool == .freehand {
+            // 画笔工具：至少需要2个点
+            isValid = (shape.points?.count ?? 0) >= 2
+        } else {
+            // 其他工具：检查宽高
+            let dx = abs(shape.endPoint.x - shape.startPoint.x)
+            let dy = abs(shape.endPoint.y - shape.startPoint.y)
+            isValid = dx > 3 || dy > 3
+        }
+        
+        if isValid {
             session.commit(shape)
             onSessionChanged?()
             // 通知形状已提交到画布（此时锁定选区）

DockMasterPro/Plugins/ScreenshotPlugin/ScreenshotEditToolbar.swift

@@ -27,8 +27,8 @@ final class ScreenshotEditToolbar: NSView {
     private static let leftPadding: CGFloat = 8
     private static let rightPadding: CGFloat = 8
 
-    // 工具按钮数量（矩形、圆形、箭头）
-    private static let toolButtonCount: Int = 3
+    // 工具按钮数量（矩形、圆形、箭头、画笔）
+    private static let toolButtonCount: Int = 4
 
     // 计算总宽度
     static var width: CGFloat {
@@ -126,6 +126,15 @@ final class ScreenshotEditToolbar: NSView {
             action: #selector(toolBtnClicked(_:))
         )
         toolButtons.append((.arrow, arrowBtn))
+        toolX += bs + gap
+        
+        let freehandBtn = addBtn(
+            systemName: "pencil.tip",
+            tooltip: L("edit.tool.freehand"),
+            frame: NSRect(x: toolX, y: cy, width: bs, height: bs),
+            action: #selector(toolBtnClicked(_:))
+        )
+        toolButtons.append((.freehand, freehandBtn))
 
         // ── Right group: undo/redo | copy cancel save ─────────────────────
         let undoRedoW  = bs + gap + bs
@@ -293,13 +302,14 @@ final class ScreenshotEditToolbar: NSView {
 
     static func L(_ key: String) -> String {
         let table: [String: [String: String]] = [
-            "edit.tool.rect":   ["en": "Rectangle",   "zh-Hans": "矩形",      "zh-Hant": "矩形",     "ja": "矩形"],
-            "edit.tool.circle": ["en": "Circle",      "zh-Hans": "圆形",      "zh-Hant": "圓形",     "ja": "円"],
-            "edit.tool.arrow":  ["en": "Arrow",       "zh-Hans": "箭头",      "zh-Hant": "箭頭",     "ja": "矢印"],
-            "edit.undo":        ["en": "Undo",        "zh-Hans": "撤销",      "zh-Hant": "復原",     "ja": "元に戻す"],
-            "edit.redo":        ["en": "Redo",        "zh-Hans": "重做",      "zh-Hant": "重做",     "ja": "やり直し"],
-            "toolbar.copy":     ["en": "Copy",        "zh-Hans": "复制",      "zh-Hant": "複製",     "ja": "コピー"],
-            "toolbar.cancel":   ["en": "Cancel",      "zh-Hans": "取消",      "zh-Hant": "取消",     "ja": "キャンセル"],
+            "edit.tool.rect":     ["en": "Rectangle",   "zh-Hans": "矩形",      "zh-Hant": "矩形",     "ja": "矩形"],
+            "edit.tool.circle":   ["en": "Circle",      "zh-Hans": "圆形",      "zh-Hant": "圓形",     "ja": "円"],
+            "edit.tool.arrow":    ["en": "Arrow",       "zh-Hans": "箭头",      "zh-Hant": "箭頭",     "ja": "矢印"],
+            "edit.tool.freehand": ["en": "Freehand",    "zh-Hans": "画笔",      "zh-Hant": "畫筆",     "ja": "ペン"],
+            "edit.undo":          ["en": "Undo",        "zh-Hans": "撤销",      "zh-Hant": "復原",     "ja": "元に戻す"],
+            "edit.redo":          ["en": "Redo",        "zh-Hans": "重做",      "zh-Hant": "重做",     "ja": "やり直し"],
+            "toolbar.copy":       ["en": "Copy",        "zh-Hans": "复制",      "zh-Hant": "複製",     "ja": "コピー"],
+            "toolbar.cancel":     ["en": "Cancel",      "zh-Hans": "取消",      "zh-Hant": "取消",     "ja": "キャンセル"],
             "toolbar.save":    ["en": "Save",         "zh-Hans": "保存",      "zh-Hant": "儲存",     "ja": "保存"],
         ]
         let pref = Locale.preferredLanguages.first ?? "en"