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/Features/Approvals/ApprovalModal.swift

@@ -5,13 +5,17 @@ import SFSafeSymbols
 /// be swiped away. The endpoint id is the trusted identity; display names are
 /// peer-provided.
 struct ApprovalModalHost: View {
+	/// Driven by the host so presentation can be deferred until any competing sheet
+	/// (the Share/QR drawer) has finished dismissing — macOS silently drops a sheet
+	/// presented while another is still animating out.
+	@Binding var isPresented: Bool
 	let state: ApprovalState
 	let onAccept: (String) -> Void
 	let onRefuse: (String) -> Void
 
 	var body: some View {
 		Color.clear
-			.sheet(isPresented: .constant(state.current != nil)) {
+			.sheet(isPresented: $isPresented) {
 				if let request = state.current {
 					ApprovalSheet(state: state, request: request, onAccept: onAccept, onRefuse: onRefuse)
 						.interactiveDismissDisabled(true)