feat(filter): add edge detection (-D flag) using Sobel operator

[swastijain132005]

Adds a new Edge Detection filter (-D flag) using the Sobel operator.
This filter highlights sharp changes in color intensity, producing a pencil-sketch-like outline of the image. It works on each color channel (R, G, B) by computing horizontal and vertical gradients with a 3×3 Sobel kernel.

Semver Changes

✅Minor (new features, no breaking changes)

Issues

Closes #24

Checklist

✅ I have read the Contributing Guidelines

✅My code follows the project style guidelines

✅I have tested the filter locally and verified it works correctly

[harshsankhla18]

Look I am not expecting you to remove // gets all filter flags and checks validity
for(int i=0; i<argc; i++){
char temp = getopt(argc,argv,filters);
if(temp == -1) break;
filterArr[i]= temp;
if(filterArr[i] == '?') {
printf("Invalid filter option");
return 1;
}
}
and adding while ((opt = getopt(argc, argv, filters)) != -1)
{
if (opt == '?')
{
printf("Usage: ./filter [flag] infile outfile\n");
return 3;
printf("Invalid filter option\n");
return 2;
}
filterArr[filterCount++] = (char)opt;
}
so dont change that in filter.c

[harshsankhla18]

@swastijain132005 Everything is fine but this opt logic changing is causing error , so remove this and work with mine written logic to check flags and also show me output.bmp in your next PR as it is having error in my vs code. In short what you need to do is keep my filter.c as it is just add D in the end of filter string and in switch case add case D(then function call inside) thats it. No extra change i filter.c would be accepted

[swastijain132005]

Okay I will fix it

[harshsankhla18]

@swastijain132005 resolve conflicts and attach screenshot of the code working , then I will merge.

[swastijain132005]

output.bmp