Complete Economic Observatory MVP (ADAPTIVE-WP-0002)

Add file-based Bubble, Stripe, and OpenRouter importers; usage attribution,
cost allocation, pricing simulator, credit wallets, and recommendations in the
dashboard API. Document whynot-design UI workflow and archive the finished
workplan with all ten tasks marked done.

projects/coulomb-pricing/observatory/importers/_io.py

@@ -0,0 +1,13 @@
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+
+def read_export(path: Path) -> dict:
+    return json.loads(path.read_text(encoding="utf-8"))
+
+
+def write_registry(path: Path, payload: dict) -> None:
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(json.dumps(payload, indent=2) + "\n", encoding="utf-8")