fix(gui): disable text selection on UI labels, add edge-scroll during drag

UI labels (status, headings, control text) no longer selectable.
Console/hex content remains selectable for copy. ScrollArea now
nudges when drag-selecting near the bottom edge (~240px/s).

crates/pipeview-gui/src/panels/plot_view.rs

@@ -1,6 +1,6 @@
 use crate::buffers::{PlotBuffer, PlotSeriesKind};
 use crate::perf::PlotRenderStats;
-use egui::{Button, Ui, vec2};
+use egui::{Button, Label, Ui, vec2};
 use egui_plot::{Legend, Line, Plot, PlotBounds, PlotPoints};
 
 #[derive(Clone, Copy, PartialEq, Eq)]
@@ -46,7 +46,7 @@ pub fn render(
             if ui.button(toggle_label).clicked() {
                 toggle_detached = true;
             }
-            ui.label("no plot data");
+            ui.add(Label::new("no plot data").selectable(false));
         });
         return PlotRenderOutput {
             stats: PlotRenderStats {