Add About window with creator and version info

Shows app icon, version, "Freeware" badge, creator (Marco Wende —
Wende.IT), and link to wende.it. Accessible via "Über Snipping Tool…"
in the menu bar.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Sources/AboutWindowController.swift

@@ -0,0 +1,73 @@
+import AppKit
+import SwiftUI
+
+final class AboutWindowController: NSWindowController, NSWindowDelegate {
+    static let shared = AboutWindowController()
+
+    private convenience init() {
+        let window = NSWindow(
+            contentRect: NSRect(x: 0, y: 0, width: 320, height: 280),
+            styleMask: [.titled, .closable],
+            backing: .buffered,
+            defer: false
+        )
+        window.title = "Über Snipping Tool"
+        window.isReleasedWhenClosed = false
+        window.center()
+        self.init(window: window)
+        window.delegate = self
+    }
+
+    func show() {
+        window?.contentView = NSHostingView(rootView: AboutView())
+        NSApplication.shared.setActivationPolicy(.regular)
+        NSApplication.shared.activate(ignoringOtherApps: true)
+        window?.makeKeyAndOrderFront(nil)
+    }
+
+    func windowWillClose(_ notification: Notification) {
+        let otherVisible = NSApplication.shared.windows.filter { $0.isVisible && $0 != window }
+        if otherVisible.isEmpty {
+            NSApplication.shared.setActivationPolicy(.accessory)
+        }
+    }
+}
+
+struct AboutView: View {
+    private let version = Bundle.main.object(forInfoDictionaryKey: "CFBundleShortVersionString") as? String ?? "1.0"
+    private let build = Bundle.main.object(forInfoDictionaryKey: "CFBundleVersion") as? String ?? "1"
+
+    var body: some View {
+        VStack(spacing: 16) {
+            if let appIcon = NSImage(named: NSImage.applicationIconName) {
+                Image(nsImage: appIcon)
+                    .resizable()
+                    .frame(width: 80, height: 80)
+            }
+
+            Text("Snipping Tool")
+                .font(.title.bold())
+
+            Text("Version \(version) (\(build))")
+                .foregroundStyle(.secondary)
+                .font(.callout)
+
+            Text("Freeware")
+                .font(.callout)
+                .padding(.horizontal, 12)
+                .padding(.vertical, 4)
+                .background(.quaternary)
+                .clipShape(Capsule())
+
+            VStack(spacing: 4) {
+                Text("Marco Wende — Wende.IT")
+                    .font(.body)
+
+                Link("wende.it", destination: URL(string: "https://wende.it")!)
+                    .font(.body)
+            }
+        }
+        .padding(30)
+        .frame(width: 320, height: 280)
+    }
+}

Sources/MenuBarContentView.swift

@@ -27,6 +27,10 @@ struct MenuBarContentView: View {
         }
         .keyboardShortcut(",")
 
+        Button("Über Snipping Tool…") {
+            AboutWindowController.shared.show()
+        }
+
         Divider()
 
         Button("Beenden") {