Append actor note to AD info field on user disable/enable

[claire-peters]

Summary

• Add _append_info_note() to LDAPConn in ldap/utils.py — reads the current AD info field, appends \nYYYY-MM-DD <role> <username> disabled/enabled via CF, and writes back; skips and logs a warning if the result would exceed 1024 characters
• Update deactivate_user() and reactivate_user() on LDAPConn to accept optional actor_username/actor_role and call _append_info_note after a successful operation
• Update remove_member_from_group() on LDAPConn to forward actor params to deactivate_user
• Thread actor info through project_preremove_projectuser and project_reactivate_projectuser signal sends in project/views.py and their receivers in ldap/signals.py
• Add _actor_role_label() helper in project/views.py to map full role names to short labels (PI, GM, AM, SM) for the note

Test plan

• Remove a user from their primary group as a PI and confirm the AD info field gains a line like 2026-06-17 PI mmcfee disabled via CF
• Reactivate that user as a GM and confirm info gains 2026-06-17 GM msyed enabled via CF
• Pad a test user's info field to near 1024 chars and confirm disable is still applied but the note write is skipped with a warning log entry
• Remove a non-primary-group user and confirm info is unchanged (no note appended for plain group removal)
• Confirm existing info content is preserved (append, not replace)