fix(clients): list HWID devices when the HWID limit is 0

EnforceHwidForSubID returned before recording anything when a sub had no
limit, so the panel's HWID Devices list stayed empty for every unlimited
client. Devices are now upserted on the (sub_id, hwid_hash) index without
enforcement or X-Hwid-* headers; the write is best-effort and only logs on
failure, so tracking can never deny a subscription nothing restricts.

internal/web/service/client_hwid_test.go

@@ -45,6 +45,23 @@ func TestClientHwidGate(t *testing.T) {
 	if !res.Allowed || res.Active {
 		t.Fatalf("no limit should allow missing HWID without active headers: %+v", res)
 	}
+
+	for _, ua := range []string{"Happ/1.0", "Happ/2.0"} {
+		res, err = svc.EnforceHwidForSubID("sub-hwid", HwidRequest{Hwid: "device-one", UserAgent: ua})
+		if err != nil {
+			t.Fatalf("no-limit gate with HWID: %v", err)
+		}
+		if res != (HwidGateResult{Allowed: true}) {
+			t.Fatalf("no limit should allow HWID without active headers: %+v", res)
+		}
+	}
+	list, err := svc.ListClientHwids("hwid@example.com")
+	if err != nil {
+		t.Fatalf("list HWIDs: %v", err)
+	}
+	if len(list) != 1 || list[0].UserAgent != "Happ/2.0" {
+		t.Fatalf("no limit should still track one device with fresh metadata, got %+v", list)
+	}
 }
 
 func TestClientHwidGateRegistersAndBlocks(t *testing.T) {