fix(tui): make inactive column names readable

Inactive column header name was brightBlack (dark gray) — indistinguishable
from the dim separator line beneath it. Change to white so column names are
legible even when not selected; the ─ underline bar stays brightBlack to
keep the visual hierarchy.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

packages/kanban/lib/src/commands/tui_command.dart

@@ -649,7 +649,7 @@ class TuiCommand extends DewCommand {
         : '  ${col.name} ($count) ';
     cells.add(_Cell(
       _trunc(nameRaw, colW).padRight(colW),
-      fg: isSelected ? color : ConsoleColor.brightBlack,
+      fg: isSelected ? color : ConsoleColor.white,
       bold: isSelected,
     ));