ui: a press anywhere in the window closes the time-window popover

The window control is a GtkMenuButton whose popover autohides -- which works for as long as
GTK holds the popover's grab, and the grab is what can go missing: a window manager moving
it, the nested popover the unit dropdown opens taking it, and every headless run, where
there is no manager to hand one out at all. After that a click anywhere else in the window
leaves the bubble up, which is the "sometimes it is awkward to close" report.

`on_window_popover_press()` states the rule outright instead of relying on the grab: any
press that reaches the window's own surface closes it. That needs no hit test beyond the
button -- a popover is its own surface, so a click *inside* it never arrives here -- and the
button is left alone, because its own click is the toggle that closes it. The press gesture
is on the window in the capture phase, so a widget under the press (the plot's own gestures
among them) cannot hide it.

[windowpop] reads both halves, with autohide turned off for the probe -- the state a user
meets when the grab goes missing:

    [windowpop] opened=1 visible=1 click_gestures=2
    [windowpop] after a press elsewhere: active=0 (want 0)
    [windowpop] after a press on the button: active=1 (want 1)

`click_gestures` is read as well as the handler, so "the rule works" and "the rule is
connected" are two facts rather than one.

docs/claude/probe-readings.md

@@ -1214,3 +1214,18 @@ builds, plus `nested` — the list being *inside* that revealer, which is the on
 (a list parented elsewhere reads 1 everywhere else). `[events]` is the other half, and it drives the pane end
 to end: recording off, recording on, the trigger, the history button that reveals it, a row click and the
 replay, then Compare and Accumulate — so the file's buttons are read by being used.
+
+## `[windowpop]`
+
+```
+[windowpop] opened=1 visible=1 click_gestures=2
+[windowpop] after a press elsewhere: active=0 (want 0)
+[windowpop] after a press on the button: active=1 (want 1)
+```
+
+`UDPSCOPE_PROBE_WINDOWPOP_MS`: the time-window popover and how it closes. Autohide is turned *off* for the
+probe, exactly as the menu probe does it -- a popover dismisses itself when GTK holds its *grab*, and a bare
+`xvfb-run` has no window manager to hand one out -- so what is measured is the state a user meets when the
+grab goes missing, where the press has to close the bubble anyway. `click_gestures` reads that the controller
+is *connected* as well as that its handler works; the last press is on the button itself, which must be left
+to its own toggle (`want 1` rather than `0`).