feat(ntfy): add the HTTP client, stream manager, and account discovery

Speak the ntfy JSON API directly: subscribe, publish, group topics that share a server and credentials, reconnect with backoff and a since cursor, and list account subscriptions, reservations, and ACL grants.

internal/ntfy/group.go

@@ -0,0 +1,52 @@
+package ntfy
+
+import (
+	"net/url"
+	"strings"
+
+	"lazyntfy/internal/config"
+)
+
+// Group is a set of topics that share an origin and credentials and can
+// therefore share one JSON stream.
+type Group struct {
+	Origin string
+	Names  []string
+	Auth   config.Auth
+}
+
+// URL is the /json subscription endpoint for this group.
+func (g Group) URL(since string) string {
+	parts := make([]string, len(g.Names))
+	for i, name := range g.Names {
+		parts[i] = url.PathEscape(name)
+	}
+	endpoint := g.Origin + "/" + strings.Join(parts, ",") + "/json"
+	if since == "" {
+		return endpoint
+	}
+	q := url.Values{}
+	q.Set("since", since)
+	return endpoint + "?" + q.Encode()
+}
+
+// PublishURL is the POST endpoint for one topic.
+func PublishURL(origin, name string) string {
+	return origin + "/" + url.PathEscape(name)
+}
+
+// GroupSubs buckets subscriptions that can share a connection.
+func GroupSubs(subs []config.Sub) []Group {
+	var out []Group
+	index := map[string]int{}
+	for _, sub := range subs {
+		key := sub.Origin + "\n" + sub.Auth.Token + "\n" + sub.Auth.User + "\n" + sub.Auth.Password
+		if i, ok := index[key]; ok {
+			out[i].Names = append(out[i].Names, sub.Name)
+			continue
+		}
+		index[key] = len(out)
+		out = append(out, Group{Origin: sub.Origin, Names: []string{sub.Name}, Auth: sub.Auth})
+	}
+	return out
+}