crossterm attaches KeyModifiers::SHIFT to every uppercase char, so a real
Shift+S delivered Char { c: 'S', shift: true }. canonical() turned that
into "shift-S", which the default "S" binding never matched, so
FastForwardSpawn was unreachable from the keyboard.
canonical() now drops the shift- prefix when the char is already
uppercase, since the case already says "shifted". Regression test drives
an actual crossterm KeyEvent through canonicalise() and the keymap,
rather than asserting on the binding string, per #70.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>