feat(mail): map standard IMAP folders per profile

docs/MAIL_HANDBOOK.md

@@ -93,6 +93,13 @@ configuration. It has a stable id, lifecycle state, scope, owner context, and
 non-secret connection metadata. Passwords are write-only encrypted values and
 are never returned through list/read/capability responses.
 
+An IMAP server may map the standard Inbox, Sent, Drafts, Trash, Archive, and
+Junk roles to exact provider folder names. These mappings belong to the reusable
+profile/server. Empty roles retain automatic behavior. The historical
+`imap.sent_folder` value is read as the Sent mapping and remains synchronized
+for compatibility; a Campaign-specific Sent override still wins for that
+Campaign.
+
 Profiles may be scoped to system, tenant, user, group, or campaign context.
 Scope controls where a profile can be discovered; effective policy can narrow
 that further. A visible profile is not automatically authorized for every
@@ -227,8 +234,10 @@ account's user scope. Grant `mail:profile:write_own` for self-service;
 `mail:profile:write` remains broad profile administration authority.
 
 1. Choose the narrowest suitable scope and a stable, descriptive name/slug.
-2. Configure SMTP, optional IMAP, TLS mode, account identity, Sent-folder
-   behavior, and timeouts. Sender/envelope/recipient constraints belong to
+2. Configure SMTP, optional IMAP, TLS mode, account identity, standard folder
+   mappings, and timeouts. Folder discovery proposes provider-visible Inbox,
+   Sent, Drafts, Trash, Archive, and Junk names without mutating the mailbox.
+   Sender/envelope/recipient constraints belong to
    effective Mail policy; Campaign rate limits remain delivery configuration.
 3. Enter credentials only in the dedicated credential fields. Returned profile
    data indicates whether credentials are configured without returning them.