feat: add KIE remaining credits node

docs/KIE_API_NANOBANANA_SPEC.md

@@ -1,5 +1,18 @@
+## Credits (official)
+GET https://api.kie.ai/api/v1/chat/credit
+Header: Authorization: Bearer YOUR_API_KEY
+
+Response:
+{
+  "code": 200,
+  "msg": "success",
+  "data": 100
+}
+- data = remaining credits (integer)
+
+
 # KIE Nano Banana Pro API (Pinned)
 - API key loaded from config/kie_key.txt
 - Create task: POST /api/v1/jobs/createTask
 - Poll task: GET /api/v1/jobs/recordInfo?taskId=
-- Credits: use remaining-credits endpoint
+- Credits: GET https://api.kie.ai/api/v1/chat/credit with header `Authorization: Bearer <token>`; expects JSON `{ "code": 200, "msg": "success", "data": <remaining_credits_int> }` and treat non-200 code as error.