Add liquidity tracking, budget, and platform cost history

Restore operator platform costs (Bubble, domains, Stripe) with monthly
history from March 2025 and member payments from November 2025. Track
€1,000 starting budget, cumulative burn, and remaining liquidity in the
economics dashboard. Document LQ requirements in REQUIREMENTS.md.

projects/coulomb-pricing/observatory/models.py

@@ -7,6 +7,7 @@ from typing import Literal
 CostCategory = Literal["fixed", "variable"]
 MemberStatus = Literal["active", "churned", "paused"]
 PricingModelStatus = Literal["active", "candidate", "retired"]
+LiquidityStatus = Literal["burning", "neutral", "generating"]
 
 
 @dataclass(frozen=True)
@@ -42,6 +43,21 @@ class CostEntry:
     allocation: str
 
 
+@dataclass(frozen=True)
+class MonthlyPlatformCost:
+    period: str
+    platform_cost: Decimal
+    active_members: int
+    gross_revenue: Decimal
+
+
+@dataclass(frozen=True)
+class Budget:
+    currency: str
+    initial_budget: Decimal
+    started: str
+
+
 @dataclass(frozen=True)
 class RevenueEntry:
     id: str
@@ -69,9 +85,24 @@ class EconomicsSnapshot:
     currency: str
     active_members: int
     monthly_revenue: Decimal
-    monthly_cost: Decimal
+    monthly_platform_cost: Decimal
     cost_per_member: Decimal
     gross_margin: Decimal
     gross_margin_pct: Decimal
     pricing_model_count: int
-    revenue_source: str
+    revenue_source: str
+    period_net_liquidity: Decimal
+    liquidity_status: LiquidityStatus
+
+
+@dataclass(frozen=True)
+class LiquiditySummary:
+    currency: str
+    through_period: str
+    initial_budget: Decimal
+    cumulative_member_payments: Decimal
+    cumulative_platform_cost: Decimal
+    cumulative_net_liquidity: Decimal
+    remaining_budget: Decimal
+    liquidity_status: LiquidityStatus
+    months_tracked: int