Fix cumulative platform cost Stripe double-counting

Split infrastructure vs payment-processing costs. Liquidity burn now
uses infrastructure cash out only (€1,155.20 cumulative) because Stripe
fees are already deducted from net member payments. Total platform cost
(€1,158.24) remains visible for gross-margin economics.

projects/coulomb-pricing/REQUIREMENTS.md

@@ -24,18 +24,27 @@ separate from platform cost accrual.
 ### LQ-003 — Budget tracking
 
 Maintain an operator liquidity budget (initial: **€1,000**) and compute
-remaining budget after cumulative platform spend minus cumulative member
-payments received.
+remaining budget after cumulative **infrastructure** spend minus cumulative net
+member payments received.
 
 ### LQ-004 — Liquidity position
 
 Report whether the project is **burning**, **neutral**, or **generating**
 liquidity each period:
 
-- `period_net = member_payments - platform_costs`
+- `period_net = net_member_payments - infrastructure_cost`
 - `cumulative_net = sum(period_net)`
 - `remaining_budget = initial_budget + cumulative_net`
 
+**No double-counting:** payment-processing fees (Stripe) are deducted from net
+member payments. They are tracked separately for economics reporting but must
+**not** be subtracted again in the liquidity formula.
+
+- `total_platform_cost = infrastructure_cost + payment_processing_cost` (for
+  gross-margin economics vs gross revenue)
+- `cumulative_total_platform_cost` is informational; liquidity burn uses
+  `cumulative_infrastructure_cost` only
+
 Negative remaining budget means the MVP has consumed more liquidity than the
 allocated budget.