Add image editor with annotation tools

Integrates an editor accessible via "Letzte Aufnahme bearbeiten…" or
"Bild bearbeiten…" in the menu bar. Supports arrow, rectangle, ellipse,
and text annotations with color picker, line width, undo/redo, and
export to file or clipboard.

New files in Sources/Editor/:
- AnnotationItem/Document: data model and state management
- AnnotationCanvasView: NSView with CG rendering and mouse interaction
- AnnotationRenderer: shared rendering for canvas and image export
- EditorToolbarView: SwiftUI toolbar with tool selection and actions
- EditorWindowController: window lifecycle following SettingsWindowController pattern

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

Sources/AppCoordinator.swift

@@ -36,6 +36,9 @@ final class AppCoordinator: ObservableObject {
         didSet { persistAndRegister(mode: .region, combo: hotKeyRegion) }
     }
 
+    @Published var lastCapturedURL: URL?
+    private var editorController: EditorWindowController?
+
     init() {
         let defaults = UserDefaults.standard
 
@@ -157,10 +160,9 @@ final class AppCoordinator: ObservableObject {
     }
 
     private func handleCaptured(at url: URL, saves: Bool, copies: Bool) {
-        guard FileManager.default.fileExists(atPath: url.path) else {
-            // User cancelled the interactive capture (Esc).
-            return
-        }
+        guard FileManager.default.fileExists(atPath: url.path) else { return }
+
+        lastCapturedURL = saves ? url : nil
 
         if copies, let image = NSImage(contentsOf: url) {
             let pasteboard = NSPasteboard.general
@@ -173,6 +175,57 @@ final class AppCoordinator: ObservableObject {
         }
     }
 
+    // MARK: - Editor
+
+    func openEditorForLastCapture() {
+        guard let url = lastCapturedURL,
+              FileManager.default.fileExists(atPath: url.path),
+              let image = NSImage(contentsOf: url) else { return }
+        openEditor(image: image, sourceURL: url)
+    }
+
+    func openEditorForFile() {
+        let panel = NSOpenPanel()
+        panel.allowedContentTypes = [.png, .jpeg, .tiff, .bmp]
+        panel.canChooseDirectories = false
+        panel.allowsMultipleSelection = false
+        guard panel.runModal() == .OK, let url = panel.url,
+              let image = NSImage(contentsOf: url) else { return }
+        openEditor(image: image, sourceURL: url)
+    }
+
+    private func openEditor(image: NSImage, sourceURL: URL) {
+        let controller = EditorWindowController(image: image, sourceURL: sourceURL) { [weak self] annotatedImage in
+            guard let self, let annotatedImage else { return }
+            self.saveAnnotatedImage(annotatedImage, replacingFileAt: sourceURL)
+        }
+        editorController = controller
+        controller.showEditor()
+    }
+
+    private func saveAnnotatedImage(_ image: NSImage, replacingFileAt url: URL) {
+        guard let tiffData = image.tiffRepresentation,
+              let bitmap = NSBitmapImageRep(data: tiffData) else { return }
+
+        let fileType: NSBitmapImageRep.FileType = imageFormat == .jpg ? .jpeg : .png
+        let properties: [NSBitmapImageRep.PropertyKey: Any] = fileType == .jpeg
+            ? [.compressionFactor: 0.9] : [:]
+
+        guard let data = bitmap.representation(using: fileType, properties: properties) else { return }
+
+        do {
+            try data.write(to: url, options: .atomic)
+        } catch {
+            NSLog("SnippingTool: failed to save annotated image: \(error)")
+        }
+
+        if outputAction.copiesToClipboard {
+            let pasteboard = NSPasteboard.general
+            pasteboard.clearContents()
+            pasteboard.writeObjects([image])
+        }
+    }
+
     private static func filename(ext: String) -> String {
         let formatter = DateFormatter()
         formatter.dateFormat = "yyyy-MM-dd 'um' HH.mm.ss"