Widens worktree nav history entries to string | 'tasks' so the titlebar
back/forward buttons and Cmd/Ctrl+Alt+Arrow shortcut work from the Tasks
page. openTaskPage records a 'tasks' entry; closeTaskPage rewinds the
index when parked on one; goBack/goForward dispatches Tasks entries via
a separate view activator to bypass openTaskPage side effects.
Co-authored-by: Orca <help@stably.ai>
