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

Made-with: Cursor

backend/openapi/path-items/claim-quote.yaml

@@ -0,0 +1,28 @@
+post:
+  tags: [Claim]
+  summary: Create claim quote (rate limited)
+  security:
+    - BearerAuth: []
+  requestBody:
+    content:
+      application/json:
+        schema:
+          type: object
+          required: [lightning_address]
+          properties:
+            lightning_address:
+              type: string
+              description: user@domain.tld
+  responses:
+    "200":
+      description: Quote
+      content:
+        application/json:
+          schema:
+            $ref: "../components/schemas/claim.yaml#/QuoteResult"
+    "403":
+      description: Not eligible or budget exceeded
+      content:
+        application/json:
+          schema:
+            $ref: "../components/schemas/common.yaml#/ApiError"