feat(screenshot): add guide line sub-mode to ruler measurement tool

- add MeasureMode.guide as the 6th ruler sub-mode; single click places
  a horizontal guide, Shift+click places a vertical guide spanning the
  full canvas width/height
- render guide as a dashed line using canvasBounds for edge-to-edge
  extent; label shows x/y coordinate in px or pt matching current unit
- encode orientation in points[0].x (>0.5 = vertical) to avoid adding
  a new shape field
- add guide button to option row (SF Symbol: line.diagonal); update
  contentWidth to accommodate 6 mode buttons
- add i18n keys for guide line in en/zh-Hans/zh-Hant/ja

Author: qianmoQ

DockMasterPro/Plugins/ScreenshotPlugin/ScreenshotAnnotationModel.swift

@@ -30,6 +30,7 @@ enum MeasureMode: Equatable {
     case coordinate  // 坐标标注（单击）
     case dimension   // 宽高标注（拖拽矩形）
     case polyline    // 折线多段距离（多次点击，双击结束）
+    case guide       // 参考线（单击放水平线，Shift+单击放垂直线，贯穿全图）
 }
 
 // MARK: - Annotation Tool
@@ -846,6 +847,39 @@ struct AnnotationShape {
                 drawPill("Σ " + distLabel(total),
                          cx: last.x, cy: last.y + capLen + labelFontSize + 6)
             }
+
+        // ── Mode 6: Guide Line ────────────────────────────────────────────
+        case .guide:
+            guard let canvas = shape.canvasBounds, canvas.width > 0, canvas.height > 0 else { return }
+            let isVertical = shape.points?.first.map { $0.x > 0.5 } ?? false
+            // points[0].x > 0.5 → vertical; otherwise horizontal (encoded at commit time)
+            let path = NSBezierPath()
+            if isVertical {
+                let x = shape.startPoint.x
+                path.move(to: NSPoint(x: x, y: canvas.minY))
+                path.line(to: NSPoint(x: x, y: canvas.maxY))
+                let labelVal = shape.rulerUnit == .px
+                    ? Int(x * shape.scaleFactor)
+                    : Int(x)
+                drawPill("x = \(labelVal)\(shape.rulerUnit == .px ? "px" : "pt")",
+                         cx: x + labelFontSize + 4,
+                         cy: canvas.minY + labelFontSize * 2)
+            } else {
+                let y = shape.startPoint.y
+                path.move(to: NSPoint(x: canvas.minX, y: y))
+                path.line(to: NSPoint(x: canvas.maxX, y: y))
+                let labelVal = shape.rulerUnit == .px
+                    ? Int(y * shape.scaleFactor)
+                    : Int(y)
+                drawPill("y = \(labelVal)\(shape.rulerUnit == .px ? "px" : "pt")",
+                         cx: canvas.minX + labelFontSize * 3 + 4,
+                         cy: y + labelFontSize / 2 + 4)
+            }
+            path.lineWidth = max(1, lw * 0.7)
+            path.setLineDash([6, 4], count: 2, phase: 0)
+            path.lineCapStyle = .round
+            color.withAlphaComponent(0.85).setStroke()
+            path.stroke()
         }
     }
 

DockMasterPro/Plugins/ScreenshotPlugin/ScreenshotAnnotationView.swift

@@ -306,6 +306,19 @@ final class ScreenshotAnnotationView: NSView, NSTextFieldDelegate {
                 shape.rulerUnit   = session.currentRulerUnit
                 session.commit(shape)
                 onSessionChanged?(); onShapeCommitted?(); needsDisplay = true
+
+            case .guide:
+                // 单击放水平线，Shift+单击放垂直线；canvasBounds 记录当前画布尺寸
+                let isVertical = event.modifierFlags.contains(.shift)
+                var shape = AnnotationShape(tool: .ruler, startPoint: pt, endPoint: pt,
+                                            color: session.currentColor, lineWidth: session.currentLineWidth,
+                                            points: [NSPoint(x: isVertical ? 1.0 : 0.0, y: 0)])
+                shape.measureMode  = .guide
+                shape.scaleFactor  = window?.screen?.backingScaleFactor ?? 1.0
+                shape.rulerUnit    = session.currentRulerUnit
+                shape.canvasBounds = bounds
+                session.commit(shape)
+                onSessionChanged?(); onShapeCommitted?(); needsDisplay = true
             case .polyline:
                 if event.clickCount == 2 {
                     // 双击：提交折线

DockMasterPro/Plugins/ScreenshotPlugin/ScreenshotEditToolbar.swift

@@ -564,7 +564,7 @@ final class ScreenshotEditOptionRow: NSView {
             let dots = CGFloat(AnnotationSession.presetColors.count) * dotSize
                      + CGFloat(AnnotationSession.presetColors.count - 1) * dotGap
             let colorSection = dots + afterDots + pickerSize
-            let modeBtns = 5 * lbSize + 4 * lbGap
+            let modeBtns = 6 * lbSize + 5 * lbGap
             let unitBtns = 2 * lbSize + lbGap
             return leftPad + colorSection + afterPicker + lbs + groupGap + modeBtns + groupGap + unitBtns + rightPad
         }
@@ -961,12 +961,13 @@ final class ScreenshotEditOptionRow: NSView {
             }
             x += Self.groupGap - Self.lbGap
 
-            // 测量模式按钮（5 种）
+            // 测量模式按钮（6 种）
             for (mode, key) in [(MeasureMode.ruler,      "edit.rl.mode.ruler"),
                                 (MeasureMode.angle,      "edit.rl.mode.angle"),
                                 (MeasureMode.coordinate, "edit.rl.mode.coord"),
                                 (MeasureMode.dimension,  "edit.rl.mode.dim"),
-                                (MeasureMode.polyline,   "edit.rl.mode.poly")] {
+                                (MeasureMode.polyline,   "edit.rl.mode.poly"),
+                                (MeasureMode.guide,      "edit.rl.mode.guide")] {
                 let btn = makeRulerModeBtn(mode: mode, tooltip: L(key),
                                            frame: NSRect(x: x, y: lbY, width: lbs, height: lbs))
                 rulerModeBtns.append((mode, btn))
@@ -1491,6 +1492,7 @@ final class ScreenshotEditOptionRow: NSView {
         case .coordinate: symbolName = "mappin"
         case .dimension:  symbolName = "arrow.left.and.right"
         case .polyline:   symbolName = "point.3.connected.trianglepath.dotted"
+        case .guide:      symbolName = "line.diagonal"
         }
         return NSImage(systemSymbolName: symbolName, accessibilityDescription: nil)
             ?? NSImage(systemSymbolName: "ruler", accessibilityDescription: nil)!
@@ -2183,6 +2185,7 @@ final class ScreenshotEditOptionRow: NSView {
             "edit.rl.mode.coord": ["en": "Coordinate", "zh-Hans": "坐标",    "zh-Hant": "座標",    "ja": "座標"],
             "edit.rl.mode.dim":   ["en": "Dimension",  "zh-Hans": "宽高",    "zh-Hant": "寬高",    "ja": "サイズ"],
             "edit.rl.mode.poly":  ["en": "Polyline",   "zh-Hans": "折线",    "zh-Hant": "折線",    "ja": "折れ線"],
+            "edit.rl.mode.guide": ["en": "Guide Line", "zh-Hans": "参考线",  "zh-Hant": "參考線",  "ja": "ガイド線"],
             "edit.rl.unit.px":    ["en": "Pixels",     "zh-Hans": "像素",    "zh-Hant": "像素",    "ja": "ピクセル"],
             "edit.rl.unit.pt":    ["en": "Points",     "zh-Hans": "点",      "zh-Hant": "點",      "ja": "ポイント"],
         ]