Reproduces breadbar's now-removed fixed Lua-widget interleave
(right-of-workspaces, left/right-of-clock, left-of-stats) as explicit
widget: slot entries, so the builtin theme still renders pixel-identical
to today's bar under breadbar's new theme-driven widget placement.
`tray` deliberately has no slot entry anywhere — it stays in the
control-panel popover regardless of [bar.slots].
Updates the one test asserting the builtin's slot contents.
92d3362a6b