Switch the primary ad account for a platform

Makes one account the primary account for its platform, the one later tools use when no account id is passed, and switches it on if it was inactive. Other active accounts stay active. When switching it on would go over the ad accounts the plan covers this billing period, the platform's previous primary is switched off to make room if that frees a place (it stays connected); otherwise the call fails with account_limit. Changes Adako settings only; nothing on the ad platform changes, so no proposal is created. Use when: the user says "use account X from now on", or a tool returned account_ambiguous or not_connected and the user confirmed which account they mean. Not for: manager accounts, which hold no campaigns. If you are unsure which account the user means, ask before switching. The account must already be known to Adako (see list_connected_accounts).