Merge pull request #29299 from AyushDas4890:fix/doc-typos-tutorials

Fix typos in tutorial documentation #29299

This PR fixes spelling typos across several tutorial documentation files (dnn, calib3d, objdetect, app, js_tutorials), including `export=dowload` -> `export=download` in the DNN text-spotting tutorial's Google Drive URLs.

Documentation-only change; no functional code is affected.

Pull Request Readiness Checklist:

[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 code under GPL or another license that is incompatible with OpenCV.

[x] The PR is proposed to the proper branch (4.x).

[x] Documentation-only change; no accuracy/performance tests or opencv_extra patch are applicable.

doc/js_tutorials/js_core/js_basic_ops/js_basic_ops.markdown

@@ -105,7 +105,7 @@ let mat = new cv.Mat();
 let matVec = new cv.MatVector();
 // Push a Mat back into MatVector
 matVec.push_back(mat);
-// Get a Mat fom MatVector
+// Get a Mat from MatVector
 let cnt = matVec.get(0);
 mat.delete(); matVec.delete(); cnt.delete();
 @endcode

doc/js_tutorials/js_imgproc/js_morphological_ops/js_morphological_ops.markdown

@@ -27,7 +27,7 @@ foreground object (Always try to keep foreground in white). So what it does? The
 through the image (as in 2D convolution). A pixel in the original image (either 1 or 0) will be
 considered 1 only if all the pixels under the kernel is 1, otherwise it is eroded (made to zero).
 
-So what happends is that, all the pixels near boundary will be discarded depending upon the size of
+So what happens is that, all the pixels near boundary will be discarded depending upon the size of
 kernel. So the thickness or size of the foreground object decreases or simply white region decreases
 in the image. It is useful for removing small white noises (as we have seen in colorspace chapter),
 detach two connected objects etc.
@@ -174,4 +174,4 @@ Try it
 <iframe src="../../js_morphological_ops_getStructuringElement.html" width="100%"
         onload="this.style.height=this.contentDocument.body.scrollHeight +'px';">
 </iframe>
-\endhtmlonly
+\endhtmlonly