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

internal/api/types.go

@@ -1,6 +1,9 @@
 package api
 
-import "time"
+import (
+	"strings"
+	"time"
+)
 
 // Alert is the server's record of what Alertmanager said. It is read-only:
 // acknowledging, assigning, noting and resolving all happen on the Incident an
@@ -147,7 +150,7 @@ const (
 	// Written by the server's notifier from the delivery result, not at enqueue.
 	// Detail carries the notification kind ("triggered", "reminder", "resolved"),
 	// and on a failure the reason after it. An absent user means the page went to
-	// the shared fallback topic rather than to a person.
+	// the shared fallback rather than to a person.
 	EventNotified     = "notified"
 	EventNotifyFailed = "notify_failed"
 )
@@ -224,20 +227,36 @@ type User struct {
 	// disabled user cannot sign in or use their keys.
 	DisabledAt *time.Time `json:"disabled_at,omitempty"`
 
-	// NtfyTopic is where this user's push notifications go. Nil and empty mean
-	// the same thing — no topic of their own — because the server stores a blank
-	// string as NULL. Their incidents fall back to the server's shared fallback
-	// topic, which carries no Acknowledge button.
-	NtfyTopic *string `json:"ntfy_topic,omitempty"`
+	// Channels are where this user's notifications go: a provider type and an
+	// address each. Only filled in for the caller's own row and, without the
+	// addresses, for an administrator's view of others. A user with none has
+	// their incidents page the server's shared fallback, which carries no
+	// Acknowledge button.
+	Channels []NotificationChannel `json:"channels,omitempty"`
 }
 
-// Topic reads the user's ntfy topic, flattening the nil and empty cases the
-// server treats alike.
-func (u User) Topic() string {
-	if u.NtfyTopic == nil {
-		return ""
+// NotificationChannel is one way of reaching a user.
+type NotificationChannel struct {
+	ID   int64  `json:"id"`
+	Type string `json:"type"`
+
+	// Address is blank unless the caller owns the channel: it can be a secret.
+	Address string `json:"address,omitempty"`
+	Enabled bool   `json:"enabled"`
+}
+
+// ChannelSummary lists the kinds of channel the user has, "ntfy, mail (off)",
+// or "" for none. Never an address.
+func (u User) ChannelSummary() string {
+	parts := make([]string, 0, len(u.Channels))
+	for _, c := range u.Channels {
+		if c.Enabled {
+			parts = append(parts, c.Type)
+		} else {
+			parts = append(parts, c.Type+" (off)")
+		}
 	}
-	return *u.NtfyTopic
+	return strings.Join(parts, ", ")
 }
 
 // IsDisabled reports whether the account has been disabled.