Add notification channels and a provider abstraction

Users get a notification_channels table (replacing users.ntfy_topic); pages fan
out to every enabled channel through a notify.Provider registry, with ntfy as
the first provider. Fallbacks are typed {type, address}. Schema edited in place:
existing databases must be recreated.

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

internal/notify/notify_test.go

@@ -0,0 +1,111 @@
+package notify_test
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"git.ryuvia.com/niklas/terdut-server/internal/notify"
+)
+
+func TestRegistry_NilAndEmptyAreEmpty(t *testing.T) {
+	var nilReg *notify.Registry
+	for name, r := range map[string]*notify.Registry{"nil": nilReg, "empty": notify.NewRegistry()} {
+		if !r.Empty() || r.Has("ntfy") || len(r.List()) != 0 {
+			t.Errorf("%s registry should be empty", name)
+		}
+		if _, ok := r.Get("ntfy"); ok {
+			t.Errorf("%s registry should have no ntfy", name)
+		}
+	}
+}
+
+func TestRegistry_ListIsOrderedByType(t *testing.T) {
+	r := notify.NewRegistry(notify.NewNtfy("http://x", ""), fakeProvider{"email"})
+	list := r.List()
+	if len(list) != 2 || list[0].Type() != "email" || list[1].Type() != "ntfy" {
+		t.Errorf("expected providers ordered by type, got %v", list)
+	}
+}
+
+type fakeProvider struct{ typ string }
+
+func (f fakeProvider) Type() string                               { return f.typ }
+func (f fakeProvider) Label() string                              { return f.typ }
+func (f fakeProvider) AddressLabel() string                       { return "" }
+func (f fakeProvider) AddressHint() string                        { return "" }
+func (f fakeProvider) Capabilities() notify.Capabilities          { return notify.Capabilities{} }
+func (f fakeProvider) Validate(a string) (string, error)          { return a, nil }
+func (f fakeProvider) Send(context.Context, notify.Message) error { return nil }
+
+func TestNtfy_ValidateTopic(t *testing.T) {
+	n := notify.NewNtfy("http://x", "")
+	for _, bad := range []string{"", "  ", "a b", "a/b", "a?b", "a#b"} {
+		if _, err := n.Validate(bad); err == nil {
+			t.Errorf("topic %q should be rejected", bad)
+		}
+	}
+	if got, err := n.Validate("  my-topic "); err != nil || got != "my-topic" {
+		t.Errorf("a good topic should be trimmed and accepted, got %q, %v", got, err)
+	}
+}
+
+func TestNtfy_SendEncodesTheMessage(t *testing.T) {
+	var got map[string]any
+	var auth string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		auth = r.Header.Get("Authorization")
+		_ = json.NewDecoder(r.Body).Decode(&got)
+	}))
+	defer srv.Close()
+
+	n := notify.NewNtfy(srv.URL+"/", "tok")
+	err := n.Send(context.Background(), notify.Message{
+		Address: "t", Kind: notify.KindTriggered, Title: "T", Body: "B", Level: 4,
+		ClickURL: "https://x/incidents/1", AckURL: "https://x/ack",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if auth != "Bearer tok" {
+		t.Errorf("expected the bearer token, got %q", auth)
+	}
+	if got["topic"] != "t" || got["title"] != "T" || got["message"] != "B" || got["priority"] != float64(5) {
+		t.Errorf("unexpected body %v", got)
+	}
+	actions, _ := got["actions"].([]any)
+	if len(actions) != 1 || actions[0].(map[string]any)["url"] != "https://x/ack" {
+		t.Errorf("expected the Acknowledge action, got %v", got["actions"])
+	}
+}
+
+func TestNtfy_ResolvedIsQuietAndTestHasNoPriority(t *testing.T) {
+	var got map[string]any
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		got = nil
+		_ = json.NewDecoder(r.Body).Decode(&got)
+	}))
+	defer srv.Close()
+	n := notify.NewNtfy(srv.URL, "")
+
+	_ = n.Send(context.Background(), notify.Message{Address: "t", Kind: notify.KindResolved, Level: 4})
+	if got["priority"] != float64(2) {
+		t.Errorf("a resolved page should be low priority whatever the severity, got %v", got["priority"])
+	}
+	_ = n.Send(context.Background(), notify.Message{Address: "t", Kind: notify.KindTest})
+	if _, ok := got["priority"]; ok {
+		t.Errorf("a test should carry no priority, got %v", got["priority"])
+	}
+}
+
+func TestNtfy_SendReportsARejection(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusForbidden)
+	}))
+	defer srv.Close()
+	if err := notify.NewNtfy(srv.URL, "").Send(context.Background(), notify.Message{Address: "t"}); err == nil {
+		t.Error("a 403 from ntfy must be an error so the notifier retries")
+	}
+}