fix(repo-appearance): collapse icon-picker buttons into a tile menu
Three trailing buttons (Choose Symbol… / Choose Image… / Clear Icon)
truncated to "Choos…" / "Clear I…" in narrow Settings windows. Drop
them and turn the preview tile itself into the action surface — a
SwiftUI `Menu` with the preview as its label. Click anywhere on the
tile and a popover lists the three options (Clear is omitted when no
icon is set, replaced by `role: .destructive` + Divider when present).
This is the macOS-native pattern (System Settings user picture,
Finder Get Info icon) so the discovery cost is low. To reinforce
clickability, the tile gains:
- a 1.5pt accentColor border on hover (animates in/out at 0.12s)
- the `.link` pointer style so the cursor switches to a pointing hand
Bumped the preview from 36pt to 40pt so the tile reads as a target
rather than a label decoration; help text for the no-icon state now
points at the tile ("Click the tile to pick a symbol or import an
image.") so users don't hunt for vanished buttons.