fix(apple): restore macOS approval modal and sandboxed file sharing

Approval modal: since the Share/QR sheet auto-opens after creating a transfer,
it is always up when a receiver request arrives, and macOS silently drops a sheet
presented while another is still dismissing — so the approval sheet never appeared.
Drive the approval sheet from explicit state (not a constant binding) and, on
macOS, defer its presentation one dismiss-beat after closing the Share/QR sheet so
the hand-off is serialized. Still a non-dismissable sheet; iOS timing unchanged.

Sandboxed file sharing: the macOS picker released its security scope immediately,
so the core's later import failed with EPERM under the App Store sandbox (the
non-sandboxed .dmg was unaffected). Capture a security-scoped bookmark at pick
time and re-acquire access across shareFiles() — during which the core imports the
bytes — mirroring the receive-folder scoped-access pattern.

apple/VniDrop/Platform/FileSystemService+macOS.swift

@@ -44,6 +44,22 @@ struct MacFileSystemService: FileSystemService {
 		guard !files.isEmpty else {
 			return .failure(InvitationError.message("Select at least one file to share"))
 		}
+		// Re-acquire security-scoped access to every picked source (from the bookmark
+		// captured at pick time) and hold it across the whole share call. The core
+		// imports the bytes during shareFiles(), so access only needs to survive that
+		// call; without this, the import fails with EPERM under the App Store sandbox.
+		var scopedURLs: [URL] = []
+		for file in files {
+			guard let bookmark = file.securityScopeBookmark else { continue }
+			var stale = false
+			guard let url = try? URL(
+				resolvingBookmarkData: bookmark, options: .withSecurityScope,
+				relativeTo: nil, bookmarkDataIsStale: &stale
+			), url.startAccessingSecurityScopedResource() else { continue }
+			scopedURLs.append(url)
+		}
+		defer { scopedURLs.forEach { $0.stopAccessingSecurityScopedResource() } }
+
 		let sources = files.map {
 			ShareSource(kind: .path, value: $0.value, displayName: $0.displayName, isDirectory: $0.isDirectory)
 		}