Fix: Never pair exclusionMode with exclusiveZone

Quickshell's exclusiveZone setter flips exclusionMode back to Normal as a
side effect, so a window declaring both is at the mercy of which property
the QML engine applies last. The 2026-09-14 Qt update changed that order
and every full-screen overlay slid under the bar.

Each overlay now declares ExclusionMode.Ignore alone. The capture picker
was the visible failure: it started under the bar, the full-output freeze
frame was squeezed into a shorter box, and every selection landed one
bar-height off in the real capture.

tests/quickshell/exclusion-idiom-contract fails any file that pairs them.

config/dot/quickshell/modules/osd/Osd.qml

@@ -29,7 +29,6 @@ PanelWindow {
     screen: root.modelData
     anchors.bottom: true
     margins.bottom: Theme.dockIconSize + Theme.dockPadding * 2 + Theme.barGap * 3
-    exclusiveZone: 0
     exclusionMode: ExclusionMode.Ignore
     implicitWidth: root.desiredWidth
     implicitHeight: 64