fix: mark the current sibling in the crumb menu with a bar

[huntharo]

Problem

The breadcrumb sibling menu marked the current folder only in bold, and
each row had both the keyboard highlight fill and an independent hover
fill. With the pointer on another row, two rows were filled and bold alone
did not say which folder you were in.

Fix

• The current row keeps an accent bar before its name, like the one beside
  the name in the Selection panel (w(space::XS), h(text::BODY),
  theme.accent); the bold stays. Every row has the bar's lane, so names
  line up.
• The separate .hover fill is gone. Entering a row with the pointer moves
  the single CrumbMenu::highlighted the arrow keys move, so only one row
  is ever filled. Only entering a row moves it: a pointer resting on a row
  does not take the highlight back after arrow-key navigation. (The menu
  scrolls, but keyboard navigation does not scroll the highlight into view
  today, so there is nothing for the pointer to fight.)
• size::SIBLING_MENU goes from 24 to 25 rem: the bar's lane plus its
  gap, so names keep the room they had.

Why a bar and not a check

The first version used a check, as the Power Efficiency menu does (#2).
There a check means the saved choice, as in any menu. This menu is for
moving around, though, and a check beside a folder reads as picked, which
is the wrong message in an app for picking what to delete. The removal
log also already uses a check beside a path to mean removed.

Before / after

Current folder Projects, pointer on Music.

Verification

• cargo xtask lint and cargo xtask test green.
• a_crumb_lists_its_siblings_and_jumps_sideways now reopens the menu,
  moves the pointer onto a non-current row, and asserts the highlight
  moved there and sibling-here lies inside the current row.
• Checked in a cargo xtask bundle build against a small demo tree
  (screenshots above).