Add workspace.tab.next / workspace.tab.previous commands that cycle the
Slots.workspace tab strip with wraparound (no-op under two tabs), bound
ctrl+pagedown / ctrl+pageup across every preset via defaultBindings. Single-
chord, so no global matcher needed. Activating a tab also focuses the
workspace slot.
Part 2 (vim gt/gT) is deferred — it needs the global multi-chord matcher
T-404 introduces. T-405 stays open for that follow-up.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>