[Improved, Fixed] Better CSV email detection

Improvements

• The CSV uploader now recognizes common alternate email headers such as “Primary Email,” “Work Email,” “Email 1/Email 2,” and more, so emails import correctly without extra setup
• The upload dialog now lists the exact columns it will import, giving users immediate confirmation that their file is mapped as expected

Fixes

• Fixed a bug where files using headers like “Primary Email” caused all candidate email addresses to be dropped during import
• The uploader now flags any column that looks like an email address but is not being imported, helping users correct header issues before launch