fix: use concrete tertiary color for row chevrons inside tinted buttons

AGENTS.md

@@ -102,8 +102,9 @@ Gotchas learned the hard way:
   .combine)` (or a Button/control) to be queryable.
 - List/Form section headers render uppercased unless `.textCase(nil)` —
   tests assert exact header strings.
-- Inside tinted Button rows, hierarchical `.primary`/`.secondary` foreground
-  styles resolve to the tint; use concrete `Color.primary`/`Color.secondary`.
+- Inside tinted Button rows, hierarchical `.primary`/`.secondary`/`.tertiary`
+  foreground styles resolve to the tint (e.g. blue chevrons); use concrete
+  `Color.primary`/`Color.secondary`/`Color(.tertiaryLabel)`.
 - The unblock confirmation dialog is queried via `app.sheets.buttons[...]`
   (a bare `buttons["Unblock"]` is ambiguous with the row label).