feat(channels): include event verb in ntfy title + smtp subject

Raise / ack / resolve all rendered with the same title and body on
ntfy and SMTP, so a recovery looked identical to the original alert.
Webhook was already fine because the JSON envelope carries 'event'.

ntfy:
  Title  '[raised · warning] dev backup_failed' (was '[warning] …')
  Tags   'raised,warning,backup_failed' (was 'warning,backup_failed')
  Body   'Resolved · <message>' / 'Acknowledged · <message>' on those events
SMTP:
  Subject '[restic-manager] [raised · warning] dev: backup_failed'

Plus: cmd/_fake_alert now accepts the ref as a positional argument
(go run ./cmd/_fake_alert steve-001) instead of silently ignoring
unknown positional args. Refuses ambiguous '-ref X positional Y'.

internal/notification/ntfy_test.go

@@ -60,13 +60,13 @@ func TestNtfySendsHeadersAndBody(t *testing.T) {
 		t.Fatalf("want 200, got %d", code)
 	}
 
-	if want := "[critical] alfa-01 check_failed"; gotTitle != want {
+	if want := "[raised · critical] alfa-01 check_failed"; gotTitle != want {
 		t.Errorf("Title: got %q want %q", gotTitle, want)
 	}
 	if gotPri != "5" {
 		t.Errorf("Priority: got %q want \"5\"", gotPri)
 	}
-	if want := "critical,check_failed"; gotTags != want {
+	if want := "raised,critical,check_failed"; gotTags != want {
 		t.Errorf("Tags: got %q want %q", gotTags, want)
 	}
 	if gotClick != "https://rm.example/a" {