fix invisible TUI cursor/buttons on serial consoles with broken color pairs

init_colors() now survives a terminal rejecting every init_pair() call
(some serial-console terminfo entries claim start_color()/COLORS support
but can't actually set custom pairs), but that exposed a follow-on bug:
the list cursor and the cert-form Continue/Cancel buttons indicated
selection purely via the COLOR_SELECTED color pair, so once that pair
silently no-ops the current row/button becomes indistinguishable from
an unselected one. Add curses.A_REVERSE alongside the color pair for
the selected state — a plain video attribute that doesn't depend on
custom-pair support, so the cursor stays visible either way.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_widgets.py

@@ -82,3 +82,15 @@ def test_init_colors_falls_back_on_serial_console():
     disabled = next(c for c in calls if c[0] == COLOR_DISABLED)
     assert normal[2] == _curses.COLOR_BLACK
     assert disabled[1:] == (_curses.COLOR_WHITE, _curses.COLOR_BLACK)
+
+def test_init_colors_survives_init_pair_rejecting_every_pair():
+    # Some serial-console terminfo entries claim start_color()/COLORS
+    # support but reject every init_pair() call (e.g. COLOR_PAIRS too
+    # small). init_colors() must not raise -- the app should still start,
+    # just without custom colors.
+    with patch.object(_curses, "start_color"), \
+         patch.object(_curses, "use_default_colors"), \
+         patch.object(_curses, "init_pair",
+                       side_effect=_curses.error("init_pair() returned ERR")), \
+         patch.object(_curses, "COLORS", 256, create=True):
+        init_colors()      # must not raise