SFTP UX improvements:
- SshKeyField: file upload button (FileReader → base64 → hidden field),
key never displayed as readable text, __KEEP_EXISTING__ sentinel
preserves DB value on re-save without re-uploading
- Auth type dropdown: password / key file / key file + passphrase
with conditional field visibility via showon
- Required field markers on host, username, path, password
- Remove insecure FTP option from remote storage dropdown
Security:
- Private key stored base64-encoded in database
- SftpUploader decodes base64 before writing temp file
- ProfileTable::store() handles sentinel to prevent key leakage
- Key content never rendered in HTML form output