scope windows: the same instruments as the main window

A scope or detached window drew its traces and nothing else: no cursors, no gate band, no trigger
marker, no measurement marks. They are not per-window state to be recreated -- the cursors are one
pair of times, the gate one band, the trigger one instant -- so the main window's row set stays the
**owner** and every window is written from it.

`sync_scope_instruments()` runs in the main tick after the main's own `sync_cursors()`/
`sync_gate()`: a gesture inside a scope window is read back from *that* window's controllers first
(those two calls only adopt while their own plot holds the grab, which is exactly "the drag
happened here"), adopted by the owner, and then every window -- the dragged one included -- is
written from the owner with the same cursor pair, mode and visibility, gate bounds and visibility,
and trigger marker. `RowSet::set_cursors()` is the new pair setter; `trigger_marker_x()`/`_visible()`
are the getters the mirror reads. The measurement marks travel by signal name
(`RowSet::MeasureMark::signal`, filled by the measures pass), so each window finds the row that
plots the signal and draws its ruler or mark there -- or none, when it does not plot it. The search
marks are times on the window and are placed on every window by the same per-frame path, and the
crosshair-axis-labels preference is restated to open windows when it changes.

Probe: `[scope-probe] instruments windows=N cursors=N gate=N trigger=N marks=N (main trigger
on=..)`, after adding a real gated `Top` measurement on `sine` -- the gate is restated visible each
frame by `update_measures()` and marks come only from `show_on_plot` measurements, so the leg uses
the app's own path. Docs: README, the cursors invariant, and the probe readings.

docs/claude/probe-readings.md

@@ -1494,6 +1494,15 @@ alone). `copied=''` with every slot empty is a copy that moved nothing. Measured
   *Reopen closed windows* item ("clicked", the item's own handler) opens every remembered one, and
   the list is empty after (`left=0`). A `remembered` that did not grow is a destroy handler that
   forgot to record; `left` non-zero is an entry the menu did not take.
+- `instruments windows=N cursors=N gate=N trigger=N marks=N` is the **one owner, every window**:
+  given a cursor pair, a gate band and the trigger marker on the main window, every scope window
+  reports the same (each count is how many windows matched). `marks` is the per-window measurement
+  mark count agreeing with what that window plots -- a window that plots the measured signal has
+  its ruler, one that does not has none. All four counts equal to `windows` is the reading;
+  `trigger` is compared against the **main** (the marker is up only while the trigger is), and the
+  parenthesis reports the main's state so a zero is distinguishable from an unequal one. The leg
+  adds a real gated `Top` measurement on `sine`, because the gate is restated visible every frame
+  by `update_measures()` and `marks` only come from `show_on_plot` measurements.
 - The second line is the **window as a drop target and a *Plot on* group**: `drop=1` is
   `on_scope_drop_channel()` — the handler the window's own target wires — putting `square` in
   the copied window's second slot (`slot1=`), the rebuild and the area's re-point then left to