Add service API for Ladill Mail large attachment uploads.

Webmail can POST /api/v1/transfers with a mailbox address to create share links for files above 25 MB.

Co-authored-by: Cursor <cursoragent@cursor.com>

deploy/shared.env.example

@@ -41,6 +41,10 @@ TRANSFER_PRICE_PER_GB_MONTH=0.15
 TRANSFER_MAX_FILE_BYTES=524288000
 TRANSFER_MAX_FILES=20
 TRANSFER_DEFAULT_RETENTION_DAYS=30
+TRANSFER_MAIL_RETENTION_DAYS=30
+
+# Ladill Mail — large attachment uploads (must match WEBMAIL_TRANSFER_API_KEY).
+TRANSFER_API_KEY_WEBMAIL=
 
 AFIA_ENABLED=true
 AFIA_PRODUCT=transfer