[l0gicgate]

Description

The chevron on the sidebar's collapsible headers sat further from the right edge than the title sits from the left, and the eject icon didn't line up with it.

• The chevron's right gap now matches the title's left gap.
• Device action icons share the chevron's size and inset, so the eject triangle's tip sits directly under the expanded chevron's tip at every text size. The release spinner uses the same column.
• The eject button no longer draws its own hover pill. The row's highlight still spans the full width, behind the icon.
• The icon sits off-centre in its 24px button, so the keyboard focus ring now wraps the icon, and a mouse click doesn't leave a ring behind.

This replaces the chevron centring from #1992, which aligned the two icons further in from the edge.

Visual evidence

N/A: agents cannot upload attachments. In words: the header's left and right gaps measure within 1px of each other, and the chevron and eject tips share a column.

How to test

1. Pin a folder and connect a removable drive so that both sidebar sections appear.
2. Hover the PINNED header and compare the gap left of the title with the gap right of the chevron.
3. Compare the tip of a drive's eject triangle with the tip of the expanded DEVICES chevron, then hover the eject icon.
4. Click into the sidebar and press Tab until the eject button has focus.
5. Repeat at a larger text size.

Expected result: the gaps match and the two tips line up at each size. Hovering the eject icon brightens it without a pill, while the row's highlight runs behind it to the row's right edge. Keyboard focus shows one compact ring around the icon.

Related issue

Closes #2059