After cross-referencing MC's button.c (lib/widget/button.c) and the
ratatui button pattern survey, two gaps remained in Phase 16:
1. MC defines NARROW_BUTTON ([X], no inner padding) — adds for
future compact toolbar/dialog use. Width formula: label + 2.
2. While width was already chars().count() (Unicode-safe CJK), no
test asserted this. Added explicit assertion: '日本語' Normal = 7,
Default = 9 cells.
Tests: 1111 passed (was 1109, +2).
Binaries rebuild clean.
Ref: MC lib/widget/button.c button_flags_t {NORMAL,DEFPUSH,NARROW,HIDDEN}.
vasilito
00bc6990eb