Add Konverter: a local-only menu bar file converter

Drag files in Finder, hold a modifier, and drop on a wheel of outputs.
Conversions run entirely on-device through ImageIO, PDFKit, AVFoundation,
the bundled CLI tools, and optional ffmpeg/LibreOffice.

Includes a --self-test suite (41 checks) and a --convert CLI mode so the
conversion matrix can be verified without the UI.

Package.swift

@@ -0,0 +1,13 @@
+// swift-tools-version: 5.9
+import PackageDescription
+
+let package = Package(
+    name: "Konverter",
+    platforms: [.macOS(.v13)],
+    targets: [
+        .executableTarget(
+            name: "Konverter",
+            path: "Sources/Konverter"
+        )
+    ]
+)