det port: comparing a group item with a numeric item is neither modelled nor measured #4671

The det port's comparison of a group (alphanumeric class) operand with a numeric item or literal has not been measured against the oracle nor modelled. Acceptance: measure cobc -std=ibm, compare with IBM's documented rule (group vs numeric: numeric treated as unsigned integer display), model it or refuse by name, add a register entry if they differ (see C13).

Found by the #4665 work (draft PR #4668, branch fix/4665-edited-compare; scratch probes in /tmp/gitgalaxy-scratch/claude/det-4665/). Part of #4270.

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