fix: the overlaid sidebar steps aside for a drag, and the compact view follows the trigger

Two reports, both real, and neither was about the lock itself.

**A drag out of an overlaid sidebar had nowhere to land.** In a window too narrow to show both columns,
`AdwOverlaySplitView` puts the sidebar *on* the plot — that is what `collapsed` means — so the pointer
stays over the list and never over a drop target: a signal could be dragged but not dropped, which reads
as "dragging does not work". `row_drag_sidebar()` now hides the sidebar on `drag-begin` and restores it on
`drag-end`, and only when collapsed: side by side the plot is already visible, and hiding the list the drag
started in would be startling. The reading begins a drag through the *source* with the state forced
collapsed, the way the sidebar probe forces it:

    pane drag: sidebar hidden for the drag=1 restored after it=1

**The compact view did not follow the trigger switch.** The locked line's first branch reads
`tc.enabled` — with trigger mode off it says `stream (trigger off)` and nothing else — and
`on_trigger_toggled()` never re-synced it, so the line kept saying whichever it had been. One call to
`sync_trigger_summary()` beside the switch sync. The dump's two `panes:` lines were already the test and
now pass it: with a session whose trigger is off, the line as found reads `stream (trigger off)` and the
live one reads the settings, because the exit probe turns the trigger on in between. Both reading `stream`
was the defect.

Verified: the two lines above; `panes: the same line as the probe found it: 'mode: stream (trigger off)'`
against the live `'signal: square | condition: window, rising | level: 0.3 .. 0.6 | mode: normal'`;
`make test-ui` 14 files; zero `Gtk-CRITICAL`. Docs: the `pane drag:` reading and the invariants bullet for
the overlay, and the `panes:` pair's second job — the refresh test — written down so the next reader knows
what both lines reading `stream` means.

docs/claude/probe-readings.md

@@ -1142,12 +1142,19 @@ library measures and draws the rect in tests of its own.
 ## `panes:` — the locked and configuration modes
 
 ```
+[udpscope]   pane drag: sidebar hidden for the drag=1 restored after it=1
 [udpscope]   pane edits: locked=document-edit-symbolic(ok) config=object-select-symbolic(ok)
 [udpscope]   panes: trigger=locked signals=locked body_visible=0 summary='signal: square | condition: window, falling | level: 0.3 .. 0.6 | mode: single | noise band: 0.2 | pre-trigger: 20 % | hold-off: 1000 ms'
 [udpscope]   panes: trigger=config signals=config body_visible=1 summary=''
 [udpscope]   panes: the same line as the probe found it: 'mode: stream (trigger off)'
 ```
 
+**`pane drag:`** is a drag begun through the *source* with the split view forced into its **overlaid**
+state, which is what a window with no room beside the plot produces. Both must read `1`: with the sidebar
+covering the plot there is no drop target under the pointer, so a drag out of the signal list is
+*impossible* rather than merely awkward, and `row_drag_sidebar()` steps the sidebar aside for the length of
+the drag and puts it back after. `hidden=0` is an overlaid drag that can never land anywhere.
+
 **`pane edits:`** is the two `[edit]` buttons in each mode, by name and verdict, and it exists because of
 a real defect: the "done" icon was `emblem-ok-symbolic`, which **Adwaita does not have** (breeze does), so
 the button that leaves configuration mode was blank — and a blank icon button is invisible in every other
@@ -1164,7 +1171,10 @@ its pane.
 - **With trigger mode off the summary is one line**: `mode: stream (trigger off)`. The four lines below
   describe a trigger that is not running, so quoting them would describe nothing. The dump carries the line
   twice — once as the probe found it and once at the end — because only a run whose *session* has the
-  trigger off shows the stream form, and a run whose session has it on shows the settings.
+  trigger off shows the stream form, and a run whose session has it on shows the settings. **The pair is
+  also the refresh test**: the probe toggles the trigger, so a run whose session has it off must show
+  `stream (trigger off)` in the line it found and the settings in the live one. Both showing `stream` is a
+  compact view that did not refresh when the mode changed, which is a defect this pair caught.
 - **`trigger panel sensitive …=1` is now a guard, not a state.** The trigger's body is never disabled —
   a trigger is configured before it is switched on — so this reads `1` always, and a `0` means the
   settings have been made unreachable again. The *cursors'* body is disabled with the cursors, and that