feat: isolate manual verification RPC usage

- add rpc node purpose support for general/manual_verify/both
- keep scan, WSS and health checks away from manual_verify nodes
- fallback manual hash verification from general RPC to manual_verify RPC
- add public cashier hash submission path and errno responses
- update tests for RPC selection, failover and manual payment flows

src/model/response/base.go

@@ -4,8 +4,11 @@ package response
 // Used for swagger documentation only — the actual response is built
 // by util/http.Resp.
 type ApiResponse struct {
-	StatusCode int         `json:"status_code" example:"200"`
-	Message    string      `json:"message" example:"success"`
-	Data       interface{} `json:"data"`
-	RequestID  string      `json:"request_id" example:"req-123456"`
+	// Stable errno used by the frontend for i18n. Success is 200; failures use codes from util/constant.Errno.
+	StatusCode int `json:"status_code" example:"200"`
+	// Default server-side errno text. Frontend should prefer status_code for display translation.
+	Message string      `json:"message" example:"success"`
+	Data    interface{} `json:"data"`
+	// Request id echoed from X-Request-ID when present.
+	RequestID string `json:"request_id" example:"req-123456"`
 }