Change the account's agency branding for white-label PDFs

Sets the account's report branding, like Settings > Report branding. Send agency_name (required the first time, up to 80 characters), accent_color (#rrggbb), contact_line (up to 120) and footer_text (up to 160); an omitted field keeps its value and null clears contact_line or footer_text. Text is stored as one plain line. remove_logo true deletes the stored logo; uploading a logo is only possible in the app. Only the account owner or an admin may change it, and the plan must include white-label reports (Scale and above). Every save raises the version, so reports and evidence packs requested afterwards are new files; files already requested keep their branding. Requires the write scope.