Add display mode chooser and align screen-sharing styles

Open the four display modes from XF86Display or the external-monitor bar icon. Reuse output reconciliation and confirmation for manual layout changes, and notify the shell when monitor state changes.

Release backdrop locks before render-element queries to prevent blurred popups from freezing the compositor. Cover popup open, update and close with regression tests.

Share translucent card styles between display modes and capture sources, show focus rings during keyboard navigation, and align picker buttons, label sizing and footer spacing with system modals.

docs/configuration.md

@@ -520,6 +520,8 @@ restores evacuated workspaces.
 ```sh
 feresectl outputs
 feresectl output-profiles
+feresectl toggle-display-mode
+feresectl output-layout extend
 feresectl output-profile presentation
 feresectl output-confirm
 feresectl output-profile auto
@@ -527,6 +529,11 @@ feresectl output-internal off
 feresectl output-revert
 ```
 
+The display Fn key (`XF86Display`) and the bar’s display icon open the same
+display-mode chooser. The icon appears while an external monitor is connected.
+`output-layout` selects a layout without requiring a named profile and keeps
+the matching profile’s mode, scale and transform settings.
+
 A manual choice overrides automatic selection until the monitor set or lid
 state changes. Reload keeps it only if its profile still exists and matches.
 Manual changes revert after `confirm-timeout` seconds unless confirmed;