feat(repo-appearance): show repo icon and color dot in the sidebar
- RepoHeaderRow renders the user-pinned icon (when set) before the repo
name via the shared RepositoryIconImage. Tinting follows the icon's
own `isTintable` rule so PNG keeps its colors and SVG/SF Symbols pick
up the repo color.
- RepositorySectionView reads `@Shared(.repositoryAppearances)` once
per row and forwards the icon + tint to RepoHeaderRow. When a color
is set it draws a Finder-style 8pt color dot at the trailing edge —
in front of the hover-revealed action buttons so the tag stays
visible at rest and shifts only slightly when the row is hovered.
- No behavior change for repos with no appearance entry: the
conditional rendering keeps the row pixel-identical to the prior
text-only layout.