Add Swagger docs at /docs and /openapi.json with split OpenAPI spec

Made-with: Cursor

backend/openapi/components/schemas/claim.yaml

@@ -0,0 +1,24 @@
+QuoteResult:
+  type: object
+  properties:
+    quote_id:
+      type: string
+    payout_sats:
+      type: integer
+    expires_at:
+      type: integer
+ConfirmResult:
+  type: object
+  properties:
+    success:
+      type: boolean
+    already_consumed:
+      type: boolean
+    payout_sats:
+      type: integer
+    next_eligible_at:
+      type: integer
+    message:
+      type: string
+    payment_hash:
+      type: string