Manage notification channels instead of an ntfy topic

Mirrors the server's channels API: add/remove channels per user from the Users
section. Requires the matching server release.

Claude-Session: https://claude.ai/code/session_016mBLURvJoMuUEr9cB2RpUN

README.md

@@ -13,7 +13,7 @@ Written in Go using [Bubbletea](https://github.com/charmbracelet/bubbletea).
 - **Teams** — switch between your teams, or see all of them at once
 - **On-call schedule** — visual calendar of who is on duty in a team, assign and remove entries
 - **Statistics** — MTTA and MTTR, plus alert frequency by name, hour and day
-- **User management** — add and remove users, manage API keys, set each user's ntfy topic
+- **User management** — add and remove users, manage API keys, manage each user's notification channels
 
 > Requires terdut-server **v0.20.0 or later**. The server became team-scoped in
 > v0.12 and this client follows it; earlier servers answer 404 for `/api/teams`
@@ -36,7 +36,7 @@ server refuses anybody else. Stats always cover all your teams; the server
 cannot narrow them to one.
 
 Administrators are the only users who can create or delete users, or act on
-someone else's password, topic or API keys. Everyone can manage their own.
+someone else's password, notification channels or API keys. Everyone can manage their own.
 
 ## Alerts and incidents
 
@@ -58,17 +58,23 @@ Two behaviours worth knowing before you press a key:
 - **Snooze is the "not now" button.** It hides an incident from the default queue
   without closing it, and expires on its own.
 
-## Push notifications
+## Notifications
 
-When the server is configured for ntfy, an incident that opens pages whoever is
-on call. Each user has their own topic, shown as a column in the Users section
-and edited with `t`. A user with no topic falls back to the server's shared
-fallback topic, which carries **no Acknowledge button** — the topic is shared, so
-a button on it would let any subscriber acknowledge as somebody else.
+When the server has a notification provider configured (ntfy today), an incident
+that opens pages whoever is on call, on every notification channel they have
+switched on. A channel is a provider type and an address (an ntfy topic); each
+user's kinds of channel are shown as a column in the Users section and managed
+with `t`: `a` adds one as `type:address` (for example `ntfy:my-topic`), `r`
+removes one by its ID. Addresses are only sent to their owner, so an
+administrator sees the kind, not where it goes. Turning a channel off is done in
+the web UI. A user with no channel falls back to the server's shared fallback,
+which carries **no Acknowledge button** — the fallback is shared, so a button on
+it would let any recipient acknowledge as somebody else.
 
-Every delivery lands on the incident's timeline: `Notified <user> (triggered)`
-when ntfy accepted the page, and `Notification to <user> failed` when it ran out
-of retries. That second one is the one to look for when nobody's phone rang.
+Every delivery lands on the incident's timeline: `Notified <user> (triggered via
+ntfy)` when the provider accepted the page, and `Notification to <user> failed`
+when it ran out of retries. That second one is the one to look for when nobody's
+phone rang.
 
 
 ## Installation
@@ -229,7 +235,7 @@ Users section:
 | Key | Action |
 |-----|--------|
 | `n` | Create a user |
-| `t` | Edit the user's ntfy topic — submit empty to clear it |
+| `t` | Manage the user's notification channels — `a` add (`type:address`), `r` remove by ID |
 | `d` | Delete a user |
 | `k` | API keys for the selected user |
 | `p` | Set the selected user's web UI password — asks for the current one when it is your own |