feat(app): implement basic function

General
- 配置界面支持配置对象存储桶
- 快捷键进入截图
- 一键上传截图 & 复制截图链接

MacOS
- 状态栏指示器和应用图标

internal/infrastructure/screencapture/capturer.go

@@ -0,0 +1,42 @@
+// Package screencapture defines the cross-platform Capturer abstraction.
+//
+// Per-platform implementations live in sibling files:
+//   - capturer_darwin.go    macOS, uses /usr/sbin/screencapture
+//   - capturer_other.go     non-darwin, uses kbinani/screenshot
+//
+// The interface is kept here so callers do not need build tags.
+package screencapture
+
+import "image"
+
+// Capturer is the abstraction that the application service depends on.
+type Capturer interface {
+	// CaptureRegion grabs the pixels within the supplied virtual-screen
+	// rectangle and returns PNG-encoded bytes.
+	CaptureRegion(rect image.Rectangle) ([]byte, error)
+
+	// VirtualBounds returns the union rectangle of every connected display.
+	VirtualBounds() image.Rectangle
+
+	// CaptureInteractive opens a system-provided region picker (e.g. macOS's
+	// `screencapture -i`) and returns the resulting PNG bytes once the user
+	// confirms a selection. If the user cancels (Esc / right-click), it
+	// returns (nil, ErrCancelled) so callers can short-circuit cleanly.
+	CaptureInteractive() ([]byte, error)
+
+	// CaptureFullScreen grabs the entire primary display silently and
+	// returns the PNG bytes. Used as the backdrop for the in-app Snipaste-
+	// style overlay; the per-region crop happens later in CropPNG once the
+	// user finishes dragging.
+	CaptureFullScreen() ([]byte, error)
+}
+
+// ErrCancelled signals that the user aborted an interactive capture.
+// It is a sentinel value; callers should compare via errors.Is.
+type cancelled struct{}
+
+func (cancelled) Error() string { return "capture cancelled by user" }
+
+// ErrCancelled is returned from CaptureInteractive when the user dismisses
+// the system selection UI without confirming a region.
+var ErrCancelled = cancelled{}