fix: resolve all golangci-lint errors

- Add error checks for w.Write, json.Encode, os.MkdirAll, os.WriteFile, file.Seek
- Fix gosimple S1000: use for range instead of for { select {} }
- Fix ineffectual assignments in adaptive_io.go
- Add nolint directives for unused code intended for future use
- Fix SA1029: use custom contextKey type instead of string
- Fix SA9003: remove empty branch in client_network_handler.go
- All linting checks now pass

cmd/server/client_network_handler.go

@@ -96,10 +96,9 @@ func (cct *ClientConnectionTracker) DetectClientConnectionType(r *http.Request)
 	}
 	
 	// Check for specific network indicators in headers
-	if xForwardedFor := r.Header.Get("X-Forwarded-For"); xForwardedFor != "" {
-		// This might indicate the client is behind a mobile carrier NAT
-		// Additional logic could be added here
-	}
+	// X-Forwarded-For might indicate client is behind a mobile carrier NAT
+	// This is noted for future enhancement
+	_ = r.Header.Get("X-Forwarded-For")
 	
 	// Check connection patterns (this would need more sophisticated logic)
 	clientIP := getClientIP(r)