Merge pull request #26373 from Kumataro:fix26372

doc: fix doxygen errors at Algorithm and QRCodeEncoder #26373

Close https://github.com/opencv/opencv/issues/26372

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/core/include/opencv2/core.hpp

@@ -3114,6 +3114,10 @@ class CV_EXPORTS Algorithm;
 template<typename _Tp, typename _EnumTp = void> struct ParamType {};
 
 
+/** @example samples/cpp/snippets/detect_blob.cpp
+An example using the BLOB to detect and filter region.
+*/
+
 /** @brief This is a base class for all more or less complex algorithms in OpenCV
 
 especially for classes of algorithms, for which there can be multiple implementations. The examples
@@ -3125,9 +3129,6 @@ etc.).
 Here is example of SimpleBlobDetector use in your application via Algorithm interface:
 @snippet snippets/core_various.cpp Algorithm
 
-@example samples/cpp/snippets/detect_blob.cpp
-An example using the BLOB to detect and filter region.
-
 */
 class CV_EXPORTS_W Algorithm
 {

modules/objdetect/include/opencv2/objdetect.hpp

@@ -87,6 +87,7 @@ namespace cv
 //! @addtogroup objdetect_qrcode
 //! @{
 
+/** @brief QR code encoder. */
 class CV_EXPORTS_W QRCodeEncoder {
 protected:
     QRCodeEncoder();  // use ::create()
@@ -151,6 +152,8 @@ public:
     CV_WRAP virtual void encodeStructuredAppend(const String& encoded_info, OutputArrayOfArrays qrcodes) = 0;
 
 };
+
+/** @brief QR code detector. */
 class CV_EXPORTS_W_SIMPLE QRCodeDetector : public GraphicalCodeDetector
 {
 public:
@@ -192,6 +195,7 @@ public:
                                               OutputArray straight_qrcode = noArray());
 };
 
+/** @brief QR code detector based on Aruco markers detection code. */
 class CV_EXPORTS_W_SIMPLE QRCodeDetectorAruco : public GraphicalCodeDetector {
 public:
     CV_WRAP QRCodeDetectorAruco();