add file/image paste to the Claude composer via native clipboard

Flutter's clipboard is text-only and tmux/send-keys carry text only, so
a pasted file or image must reach Claude as an @path reference (per the
T-134 spike). A native clide/clipboard MethodChannel reads the non-text
clipboard: GTK (gtk_clipboard_wait_for_image/uris) on Linux, NSPasteboard
on macOS. The composer overrides PasteTextIntent — Ctrl/Cmd+V resolves a
file path or writes a clipboard image to a cache dir, inserts the @path,
and falls back to plain-text paste otherwise. No new package dependency.

macOS handler is written but unverified on this Linux box — needs a build
on a Mac. Linux path builds and is covered by tests.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

macos/Runner/AppDelegate.swift

@@ -64,5 +64,35 @@ class AppDelegate: FlutterAppDelegate {
         result(FlutterMethodNotImplemented)
       }
     }
+
+    // T-138: native clipboard image/file reads. Flutter's built-in
+    // clipboard is text-only; the composer turns a pasted file or image
+    // into a Claude `@path` reference, which needs the non-text pasteboard
+    // contents read here.
+    let clipboardChannel = FlutterMethodChannel(
+      name: "clide/clipboard",
+      binaryMessenger: flutterVC.engine.binaryMessenger)
+
+    clipboardChannel.setMethodCallHandler { (call, result) in
+      let pasteboard = NSPasteboard.general
+      switch call.method {
+      case "readImage":
+        if let image = NSImage(pasteboard: pasteboard),
+           let tiff = image.tiffRepresentation,
+           let rep = NSBitmapImageRep(data: tiff),
+           let png = rep.representation(using: .png, properties: [:]) {
+          result(FlutterStandardTypedData(bytes: png))
+        } else {
+          result(nil)
+        }
+      case "readFiles":
+        let urls = pasteboard.readObjects(
+          forClasses: [NSURL.self],
+          options: [.urlReadingFileURLsOnly: true]) as? [URL] ?? []
+        result(urls.map { $0.path })
+      default:
+        result(FlutterMethodNotImplemented)
+      }
+    }
   }
 }