收紧绘图设置为两页，并把 FN 牛顿下限固定为 0。

手指 2D 方向改到 ArrowPanel 设置对话框；归零阈值不变。已用 display_prefs、finger_2d_orientation 与绘图对话框相关 smoke 测试验证。

apps/studio/tests/test_ui_smoke.py

@@ -3044,22 +3044,24 @@ def test_the_dialog_writes_the_keys_the_session_reads_back(qt_app):
 
 
 def test_the_plot_dialog_carries_the_ranges_and_the_zero_threshold(qt_app):
-    """FN has a lower bound (which may be negative); both units a deadband."""
+    """Newton FN floor is fixed at 0; both units keep a deadband."""
     from orisys_studio.ui.plot_settings_dialog import PlotSettingsDialog
 
     dialog = PlotSettingsDialog(
         units="newton", fn_min=-2.0, fn_max=6.0, deadband_n=0.25, deadband_raw=2000.0
     )
-    assert dialog.settings()["fn_min"] == -2.0
+    assert dialog.settings()["fn_min"] == 0.0
     assert dialog.settings()["fn_max"] == 6.0
     assert dialog.deadbands() == {"deadband_n": 0.25, "deadband_raw": 2000.0}
+    assert dialog.tabs.count() == 2
     # Only the half that belongs to the unit being shown can be edited.
-    assert dialog.fn_min_spin.isEnabled() and not dialog.fn_raw_min_spin.isEnabled()
+    assert dialog.fn_max_spin.isEnabled() and not dialog.fn_raw_min_spin.isEnabled()
     assert dialog.deadband_n_spin.isEnabled()
     assert not dialog.deadband_raw_spin.isEnabled()
+    assert not hasattr(dialog, "fn_min_spin")
 
     raw = PlotSettingsDialog(units="raw")
-    assert raw.fn_raw_min_spin.isEnabled() and not raw.fn_min_spin.isEnabled()
+    assert raw.fn_raw_min_spin.isEnabled() and not raw.fn_max_spin.isEnabled()
     assert raw.deadband_raw_spin.isEnabled() and not raw.deadband_n_spin.isEnabled()
     raw.fn_raw_min_spin.setValue(-50000.0)
     raw.deadband_raw_spin.setValue(5000.0)
@@ -3094,17 +3096,17 @@ def test_the_plot_dialog_values_reach_the_chart(make_window):
     window.display_ctl.apply_plot_settings(dialog.settings())
 
     plots = window.force_plots
-    assert (plots._fn_min, plots._fn_max, plots._shear_max) == (-2.0, 6.0, 3.0)
+    assert (plots._fn_min, plots._fn_max, plots._shear_max) == (0.0, 6.0, 3.0)
     assert (plots._fn_raw_min, plots._fn_raw_max, plots._shear_raw_max) == (
         -1000.0, 5e5, 2e5,
     )
     assert plots.presentation.min_deadband_for("N") == 0.25
     assert plots.presentation.min_deadband_for("raw") == 3000.0
-    assert window.prefs["plot_fn_min"] == -2.0
+    assert window.prefs["plot_fn_min"] == 0.0
     assert window.prefs["plot_deadband_raw"] == 3000.0
     assert plots.history.window_sec == 6.0
     # And the dialog would open on the same numbers next time.
-    assert window.display_ctl.plot_settings()["fn_min"] == -2.0
+    assert window.display_ctl.plot_settings()["fn_min"] == 0.0
     window.close()