[Feature Request] Add QR code scanner to subscribe to topics

Typing this kind of string by hand on a phone is painful. A QR scanner would make the subscription process much faster and less error-prone.

The natural flow would be:

1. Tap the "..." button in the app
2. Choose "Scan QR code"
3. Scan a QR code containing either:
   • a full deep link such as ntfy://ntfy.sh/mytopic, or
   • just the topic name
4. The app automatically fills in the server and topic, then subscribes

Notes

• I'm aware that the Android app registers the ntfy:// deep link scheme, but that only helps when the user taps a link. It does not help when the user is looking at a QR code on another screen or in a web page.
• A scanner inside the app would avoid relying on the system camera or a third-party scanner app to correctly route the ntfy:// URI to ntfy.
• If possible, it would be great if the scanner also supported plain text QR codes containing only the topic name (and optionally the server URL).

Environment

• App: ntfy Android
• Android version: 1.25.2
• Server: ntfy.sh