Add the Config view: edit and save the settings, applied without a restart

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/sabnzbd/sabnzbd_test.go

@@ -122,3 +122,22 @@ func TestTransportErrorHidesAPIKey(t *testing.T) {
 		t.Errorf("error leaks API key: %v", err)
 	}
 }
+
+func TestReconfigure(t *testing.T) {
+	var gotKey string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotKey = r.URL.Query().Get("apikey")
+		w.Write([]byte(`{"version":"5.1"}`))
+	}))
+	defer srv.Close()
+
+	c := NewClient("http://127.0.0.1:1", "old") // unreachable until reconfigured
+	if _, err := c.Version(context.Background()); err == nil {
+		t.Fatal("expected a connection error")
+	}
+	c.Reconfigure(srv.URL+"/", "new")
+	v, err := c.Version(context.Background())
+	if err != nil || v != "5.1" || gotKey != "new" {
+		t.Errorf("version=%q key=%q err=%v", v, gotKey, err)
+	}
+}