ui: the signal badge is the drag handle (to a plot row, or to reorder); the list rows stop dragging

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

README.md

@@ -2252,7 +2252,7 @@ exists; it is there rather than on the chip because a second gesture on a one-gl
 not something anybody would find. The chooser is opened by a `GtkGestureClick` on the existing
 label rather than by wrapping it in a `GtkButton`, because a button's padding is exactly what
 made this row twice as tall once (below), and the gesture claims its sequence so a click on the
-chip cannot become the start of a row drag.
+chip cannot also activate the row (and open its page).
 
 A `GtkSwitch` and two
 always-visible buttons made a row about twice as tall (46 px against 26 px now),
@@ -2261,7 +2261,7 @@ button and list-row minimums, not the widgets themselves, set that height, so th
 row carries a `.udpscope-compact` style class that relaxes them.
 
 **Signals start disabled**, because enabling one is what starts acquiring it.
-Enable a signal with its checkbox, or drag it onto a plot: the drop enables the
+Enable a signal with its checkbox, or drag its badge from the badge bar onto a plot: the drop enables the
 signal if needed, binds it to that row's first free trace slot, and rebuilds the
 figure so the legend name is right (there is one widget, so the row a drop lands
 on is `PlotArea::row_at()`). The status line reports the outcome of a drop