Enable generated campaign passwords

docs/CAMPAIGN_HANDBOOK.md

@@ -124,6 +124,12 @@ action.
 5. Open **Mail settings** and select an available Mail profile. The campaign
    stores only `server.mail_profile_id`; it never accepts SMTP/IMAP settings,
    usernames, passwords, or credential references.
+   If the selected profile permits a campaign-scoped Mail credential, that
+   credential remains Mail-owned even though it is created from this surface.
+   For that credential and for password-valued campaign fields, the shared
+   password generator keeps its candidate separate from the form until **Use
+   password** is explicitly confirmed. Copying a candidate does not save or
+   submit it.
 6. Save the editable version, validate the relevant sections, and resolve every
    blocking issue. Warnings remain explicit review decisions.
 7. Build the exact messages and inspect recipient, addressing, template,