Active clients per month (services Home)

#1967 "Active clients" tile on a services company's Home. For each of the last twelve months (eleven completed months plus the current month to date, UTC), the number of distinct clients whose net POSTED operating revenue in that month is positive. Operating revenue leaves out other income (4100-style) and 4999 Uncategorized Income, as the Books hub does; closing entries are excluded. A revenue entry's client is the AR customer record its invoice provenance names, else the customer its source receipt names (a Stripe cus_ id or the receipt name, folded onto the matching customer record). A payment that only settles A/R posts no revenue and never counts; a processor payout names no client. When any of a month's revenue has no client, that month is unattributed_revenue with activeClients: null, never an undercount.