macOS: Fix launch-at-login registration. #310

Pasted 1.0.1 can save Launch automatically after logging into macOS as enabled without registering a working macOS login item.

The frontend calls Tauri's autostart enable and disable commands, but the desktop capability does not grant either command. The rejected promise is only written to the webview console, so the persisted Pasted setting and the operating-system registration can disagree.

The configured AppleScript launcher also drops Pasted's --autostart argument. That prevents the application from recognizing a login launch even if registration succeeds.

Steps to reproduce:

1. Install and open Pasted 1.0.1 on macOS.
2. Enable Launch automatically after logging into macOS.
3. Log out and back in.

Pasted does not launch. System Settings may retain background-task metadata for Pasted, but System Events has no active Pasted login item.

Expected behavior:

• Enabling the setting registers Pasted for login startup.
• Disabling it removes that registration.
• Login launches retain the --autostart marker.
• Automated contract coverage prevents the capability or launcher configuration from regressing.