Open CIS Manager Organisation

Opens a CIS Manager organisation again from the organisation's code alone, for a user CIS Manager sent back because their access to it lapsed: finds the client linked to it in the signed-in user's practices, checks they can still see that client, makes them a member and grants a restricted user the organisation again, then returns where to open it: its landing page, or the page at path on its host (e.g. /returns/2026/4). 404 when none of their practices has it or they can no longer see the client; 400 for a path that is not one.

Requires: ViewAll on ProductAccounts.