Per sigprof's review feedback, extract the duplicated token substitution
logic into a single resolve_module_token() helper in constants.py.
This addresses two review comments:
1. Duplication between ModuleCommonForm.clean() and resolve_name()
2. Duplication between resolve_name() and resolve_label()
Benefits:
- Single source of truth for substitution logic
- MODULE_TOKEN_SEPARATOR constant for future configurability
- Cleaner, more maintainable code (-7 net lines)
- Easier to modify separator handling in one place