[plan] Customers section: operator manages every customer

_Automatically composed from the parent epic at dispatch time._

Split by surface, following architecture C1–C8, with C6 split into comps (C6a) and billed (C6b): 9 coders, 4 phases, one migration per wave. C7 now waits on C1 (critic fix). Replaced a prior decomposition (9 prior child(ren) archived — my own first append).