feat: implement locale.rs system module

[adolago]

Summary

A locale module for managing system locale settings is missing from the core module set. This is a minor gap — Ansible provides a similar locale_gen module.

Expected functionality

• Set system locale (LANG, LC_ALL, etc.)
• Generate locales (locale-gen on Debian, localedef on RHEL)
• Support check_mode
• Remote execution via connection

Reference

• Ansible community.general.locale_gen module
• Similar to existing timezone.rs and hostname.rs modules in approach

Acceptance criteria

• src/modules/locale.rs created with Module trait implementation
• Registered in src/modules/mod.rs
• Supports Debian-family (locale-gen) and RHEL-family (localedef)
• Unit tests included
• Check mode supported

Priority

Low — not blocking for beta