Theme role for pinned sidebar threads (sidebarRowPinned)

[flaviobarci]

Problem

Pinned threads look the same as every other row in the sidebar. The only difference is the small pin icon, which is hard to spot when scanning a long list. Right now themes can't change this, because no color role targets pinned rows.

Proposal

Add an optional theme color role, sidebarRowPinned, used as the background for rows where pinnedAt is set.

• It's optional: if a theme leaves it out, it falls back to the current row background, so existing themes look exactly the same.
• It goes in the existing "Sidebar selection" family in the theme editor, next to sidebarRowHover, sidebarRowActive and sidebarRowSelected.
• Hover, active and selected states still take priority over it.
• For imported VS Code themes, it could stay unset (no obvious VS Code key maps to it).

Example

"sidebarRowPinned": "#f9e2af1a"

In Catppuccin Mocha, that's a faint yellow tint that marks pinned rows without competing with the selected row.

Alternatives considered

• A pinned section header or divider: this changes the layout, which is a bigger product decision.
• Tinting the pin icon: helps a little, but it's still hard to see while scanning.

Related

A smaller step toward #14180: a theme role for pinned rows only, with no per-thread color picker. #8218 covers per-environment sidebar colors.