citty parses string options greedily, so a bare --frame-check consumed
the following flag as its value (--caption-zone silently dropped,
--json disabled) and failed with an error blaming --caption-zone.
Normalize rawArgs at the check command boundary (bare --frame-check
followed by a flag or at end becomes --frame-check=), attribute
frame-check spec errors to --frame-check, and detect dash-prefixed
values with corrective guidance.
Fixes#2965
