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/invariants-gtk-and-chrome.md

@@ -188,6 +188,13 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   **tooltip and accessible name** from the page's name, then hides the empty label that would otherwise
   leave the icon off-centre. An icon-only pill is still a named control for a screen reader, and
   `switcher: … pills=2 labels=0 names=2` is the reading for all three facts at once.
+- **An *overlaid* sidebar covers the plot, so a drag out of it has nowhere to land.** `collapsed` in an
+  `AdwOverlaySplitView` means the sidebar sits *on* the plot rather than beside it: the pointer is over the
+  list, never over a drop target, and a signal can be dragged but not dropped. `row_drag_sidebar()` hides
+  the sidebar on `drag-begin` and restores it on `drag-end` — only when collapsed, because side by side the
+  plot is already visible and hiding the list the drag started in would be startling. `pane drag: sidebar
+  hidden for the drag=1 restored after it=1` is the reading; the state is forced collapsed the way the
+  sidebar probe forces it.
 - **A stock icon name has to be one *Adwaita* has, and a blank button is the failure mode.** The two
   panes' `[edit]` buttons are `document-edit-symbolic` (the pencil: edit) and `object-select-symbolic`
   (the check: done). The done one was `emblem-ok-symbolic`, which breeze ships and **Adwaita does not** —