Offboard a Microsoft 365 user

Write a PowerShell 7 script Offboard-User.ps1 using the Microsoft Graph PowerShell SDK (Microsoft.Graph modules) that offboards a departing employee. Parameters: -UserPrincipalName (mandatory), -ManagerUpn (for mailbox delegation and OneDrive access), -ConvertToShared (switch), -WhatIf support. Steps: block sign-in, revoke all sessions, reset the password to a random value that is never displayed, remove from all groups except dynamic ones (report those), remove licenses, set an out-of-office reply, grant the manager full access to the mailbox, convert the mailbox to shared if requested (note that Exchange Online cmdlets are needed and connect accordingly), remove the user's MFA methods, and write a summary object plus a CSV audit log with timestamps. Handle the case where the user does not exist. Do not delete the account. Use approved verbs, comment-based help, and Write-Verbose for each step. Return only the script in one code block.