WebSocket transport for ExNtfy.Subscription (format: :ws), subscribing via GET /<topics>/ws — requires the optional :mint_web_socket dependency:

{:mint_web_socket, "~> 1.0"}

Implements the subscription's internal transport contract (Mint connect → WebSocket upgrade; each text frame is one complete JSON message object, so there is no line reassembly). Server pings are answered with pongs internally; close frames and transport errors go through the subscription's normal reconnect flow. Binary frames are ignored (ntfy sends text).

Auth works both ways on the upgrade request: the Authorization header, or auth_via: :query for the ?auth= parameter — the canonical use case for the query encoding.