A direct ACTION_VIEW intent to nostrsigner: (Browser::open from the app)
lacks category.BROWSABLE, so Amber routes it into its app-to-app path
and rejects it as malformed. The app instead opens /auth/mobile/nostr in
an in-app browser; that page fires the signer via window.location, so
the intent carries BROWSABLE and Amber uses its web-signing flow. No
visible login UI, local signing, token returned via the App Link.
HolgerHatGarKeineNode