ui: a signal's page shows gain and offset as aligned rows with a pencil each, replacing Calibrate

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ui_app.hpp

@@ -1711,7 +1711,9 @@ void on_trigger_signal_changed(GObject* obj, GParamSpec*, gpointer user);
 void show_info_dialog(GtkWindow* parent, const SignalInfo& sig);
 void on_info_clicked(GtkButton* button, gpointer user);
 void on_calibrate_apply(GtkButton*, gpointer user);
-void open_calibration(App& app, GtkWindow* parent, std::size_t signal);
+/// Which of the calibration's two numbers a dialog edits; `Both` is the full dialog.
+enum class CalibField { Both, Gain, Offset };
+void open_calibration(App& app, GtkWindow* parent, std::size_t signal, CalibField field = CalibField::Both);
 GdkContentProvider* on_drag_prepare(GtkDragSource*, double, double, gpointer user);
 int signal_color_index(const std::vector<SignalInfo>& signals, std::size_t signal);
 std::string color_hex(plot::Color c);