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

Made-with: Cursor

backend/openapi/path-items/deposit-redeem-cashu.yaml

@@ -0,0 +1,48 @@
+post:
+  tags: [Public]
+  summary: Redeem Cashu token
+  requestBody:
+    required: true
+    content:
+      application/json:
+        schema:
+          type: object
+          required: [token]
+          properties:
+            token:
+              type: string
+              description: Cashu token (cashuA... or cashuB...)
+  responses:
+    "200":
+      description: Redeem result
+      content:
+        application/json:
+          schema:
+            type: object
+            properties:
+              success:
+                type: boolean
+              paid:
+                type: boolean
+              amount:
+                type: integer
+              invoiceAmount:
+                type: integer
+              netAmount:
+                type: integer
+              to:
+                type: string
+              message:
+                type: string
+    "400":
+      description: Invalid token or address
+      content:
+        application/json:
+          schema:
+            $ref: "../components/schemas/common.yaml#/ApiError"
+    "502":
+      description: Redeem failed
+      content:
+        application/json:
+          schema:
+            $ref: "../components/schemas/common.yaml#/ApiError"