Submodule READMEs understate Drupal core support as ^11.1

Problem/Motivation

The Requirements section of both submodule READMEs lists Drupal core ^11.1:

• modules/entity_segment_user/README.md
• modules/entity_segment_group/README.md

This contradicts the modules themselves. Every .info.yml in the project — the base and all three submodules — declares core_version_requirement: '^11.1 || ^12', and the base README.md documents ^11.1 || ^12. Drupal 12 support shipped in 1.0.0-alpha1.

A reader who lands on a submodule README concludes that submodule is Drupal 11 only, which is wrong.

Proposed resolution

Update the Requirements section in both submodule READMEs to Drupal core ^11.1 || ^12, matching their .info.yml.

For entity_segment_group, also link the base README's Drupal 12 limitations section. The module's own code is Drupal 12 ready, but its phpunit (next major) job cannot pass while drupal/group is incompatible with Drupal 12. Stating the constraint without that pointer would over-promise.

Remaining tasks

• Update both Requirements sections.
• Add the Drupal 12 limitations cross-reference to the Group submodule README.
• Decide whether entity_segment_crm — the only submodule with no README — should get one; it carries the same upstream Drupal 12 caveat via drupal/crm and drupal:telephone. Split to its own issue if it grows beyond a stub.

User interface changes

None.

API changes

None. Documentation only; no core_version_requirement is changed, since those are already correct.

Data model changes

None.