Split view: defocused pane shows a placeholder instead of its content #27

When a pane is not focused in a split layout, non-table tabs (e.g. the Query Editor) render a generic "Click this pane to focus it and interact with this view" placeholder instead of showing the actual content.

Expected
A defocused pane should still show its real content read-only — e.g. a SQL/Query Editor pane should display its query text and last results, like table panes already do.

Addressed by #21.