Add Economic Observatory web UI with ledger-backed API

Introduce ui/ dashboard (dark observatory layout), JSON API, and local
dev server. All metrics load from expense and payment record ledgers.
Links Claude design reference for visual alignment.

projects/coulomb-pricing/observatory/api.py

@@ -0,0 +1,98 @@
+from __future__ import annotations
+
+import json
+from decimal import Decimal
+from pathlib import Path
+from typing import Any
+
+from .economics import build_liquidity_summary, build_snapshot
+from .load import (
+    default_data_dir,
+    latest_period,
+    load_budget,
+    load_expense_records,
+    load_membership,
+    load_monthly_ledger,
+    load_payment_records,
+    load_pricing_models,
+    load_product,
+)
+
+
+def _serialize(value: Any) -> Any:
+    if isinstance(value, Decimal):
+        return str(value)
+    if hasattr(value, "__dataclass_fields__"):
+        return {key: _serialize(getattr(value, key)) for key in value.__dataclass_fields__}
+    if isinstance(value, list):
+        return [_serialize(item) for item in value]
+    if isinstance(value, dict):
+        return {key: _serialize(item) for key, item in value.items()}
+    return value
+
+
+def _load_json_catalog(data_dir: Path, name: str) -> dict:
+    path = data_dir / "infrastructure" / name
+    if not path.exists():
+        return {}
+    return json.loads(path.read_text(encoding="utf-8"))
+
+
+def build_dashboard_payload(data_dir: Path | None = None, period: str | None = None) -> dict:
+    root = data_dir or default_data_dir()
+    product = load_product(root)
+    budget = load_budget(root)
+    models = load_pricing_models(root)
+    members = load_membership(root)
+    payments = load_payment_records(root)
+    expenses = load_expense_records(root)
+    ledger = load_monthly_ledger(root)
+    target_period = period or latest_period(ledger)
+
+    snapshot = build_snapshot(target_period, product, models, members, payments, ledger)
+    liquidity = build_liquidity_summary(budget, payments, ledger, target_period)
+    payment_by_period = {record.period: record for record in payments}
+
+    history = []
+    for month in sorted(ledger, key=lambda row: row.period):
+        if month.period > target_period:
+            continue
+        payment = payment_by_period.get(month.period)
+        net_payment = payment.net_amount if payment else Decimal("0")
+        history.append(
+            {
+                "period": month.period,
+                "active_members": month.active_members,
+                "gross_revenue": month.gross_revenue,
+                "infrastructure_cost": month.infrastructure_cost,
+                "payment_processing_cost": month.payment_processing_cost,
+                "total_platform_cost": month.total_platform_cost,
+                "net_payment": net_payment,
+                "net_liquidity": net_payment - month.infrastructure_cost,
+            }
+        )
+
+    return _serialize(
+        {
+            "design_reference": "https://claude.ai/design/p/fb2eef8c-c1fc-4c75-bff4-3782552e5511",
+            "period": target_period,
+            "product": product,
+            "budget": budget,
+            "snapshot": snapshot,
+            "liquidity": liquidity,
+            "history": history,
+            "pricing_models": models,
+            "members": members,
+            "payments": payments,
+            "expense_record_count": len(expenses),
+            "infrastructure": {
+                "domains": _load_json_catalog(root, "domains.json"),
+                "virtual_servers": _load_json_catalog(root, "virtual_servers.json"),
+                "stripe": _load_json_catalog(root, "stripe.json"),
+            },
+        }
+    )
+
+
+def payload_json(data_dir: Path | None = None, period: str | None = None) -> str:
+    return json.dumps(build_dashboard_payload(data_dir, period), indent=2)