Contact import from CSV and XLSX files

Webmail now supports bulk contact imports from CSV and XLSX files. After uploading a file, users are guided through a column mapping flow to ensure data is imported to the correct contact fields. The feature handles files up to 5MB or 5,000 rows, and when import errors occur, users see which rows failed and why, along with a success count. This reduces manual data entry when users migrate their contacts to Webmail.