Separate gettext domains from registered-string context

Software gettext strings are identified by text domain, msgid, optional context, and plural form. POM Translate registered strings use a stable registration name plus source value.

The legacy group argument accepted by pom_translate_register_string() is not currently stored as a separate lookup dimension. Do not rely on it to distinguish two meanings of identical source text; choose distinct stable names and, where appropriate, different source wording.

Use gettext context functions for software strings that ship in PO/MO catalogs. Use registered strings for site-managed public wording.

Keep printf placeholders, merge tags, and protected HTML markers unchanged in both systems. Context helps translators understand meaning but does not authorize changing runtime tokens.