Rework `FooterWidget::status_line_spans` so the footer never wraps
mid-hint at any width. Hints now drop in priority order:
1. mode label (always visible; truncated only as a last resort)
2. model name (always visible alongside mode; truncated mid-word only
after status has already been dropped)
3. status label ("working", "draft", "refreshing context", ...) — drops
first when space is tight
Previously the model name would ellipsize the moment a long status
label crowded the line, even at 60–80 columns. The new tier system
keeps mode + model intact down to ~25 cols and only falls back to
mode-only on extreme narrow widths.
Includes snapshot-style tests at widths 40, 60, 80, 100, 120 covering
the full / drop-status / truncate-model / mode-only tiers.
Fixes#88
Hunter Bown
bf2a1765fa