Sign in on macOS without the Decentraland launcher installed

The deep-link sign-in (the flow that replaced `dcl_personal_sign`) needs something on the machine to receive `decentraland://` links. On macOS the explorer currently asks the user to install the Decentraland launcher, because only an app bundle can claim a scheme and the URL is delivered as an Apple Event rather than on argv.

Handling it ourselves would mean:

- add `decentraland` to `CFBundleURLTypes` in `deploy/macos/Info.plist` (the bundle already claims an unused `dclbevyexplorer` scheme)
- register a `GURL` Apple Event handler with `NSAppleEventManager` before winit's run loop starts (an objc2 `define_class!` with one selector; objc2 and objc2-foundation are already in the tree via winit), which writes a sign-in link to the launcher bridge file the same way the windows/linux handler process does
- deal with scheme competition: with both us and the launcher claiming `decentraland`, Launch Services picks whichever registered last, and the launcher never reclaims. The polite version calls the deprecated `LSSetDefaultHandlerForURLScheme` on every start, naming the launcher when it is installed and ourselves otherwise. That is fragile and is the main reason this was not done in #1238.
- cold-start place links arrive as an event after the boot location was chosen, so they need the teleport-in-place handling too

There is no working native macOS build to test any of this against right now.

The cleaner end state is our own scheme everywhere: a `deepLink` target-config entry for bevy in decentraland/auth pointing at `dclbevyexplorer://`, registered on every OS without competing with the launcher. That still needs the Apple Event handler on macOS, but removes the competition and the launcher dependency.