useNotification opens its business API

Added

• Three APIs, along the product's own parts. apps publishes and edits apps, subscribers shows who subscribed, messages sends and keeps the history. Each one answers on its own subdomain under api.usenotification.artim-industries.com and carries its own scopes.
• The webhook lives inside the app. Set the delivery address and its secret on the app itself; new subscriptions inherit both. Reading it takes its own scope — whoever may read an app does not thereby see where it delivers.
• The API key, readable and rotatable. The key a trigger checks can be read and replaced through the API. Rotation has no overlap: the old key stops working with the answer.
• Broadcasts. The same notification to every subscriber of an app, in one call — one round trip to Expo per hundred devices, not one per recipient.
• Sign-in and consent through artim/dev. The account that owns the apps signs in at useNotification; the console never sees a password. A token is bound to exactly one publisher, and foreign apps do not exist for it.

Unchanged on purpose

• What the app does for its users stays in the app. Signing up, signing in, subscribing and reading one's own notifications have no scope and no endpoint here. Those belong to the person using the app, not to the company publishing it.
• Two scopes need Enterprise. Reading an app key and reading a subscriber's profile — one is a secret that triggers on its own, the other is somebody else's name and address.