Create a Framebuffer and Write a PPM Image

Write a C program that creates a framebuffer and outputs it in PPM format.

Requirements:

• Define a framebuffer as a 2D array of 3 unsigned chars per pixel (RGB)
• Create a framebuffer of size 8x8 pixels (64 pixels total)
• Fill the framebuffer with a gradient: red increases from left to right, green increases from top to bottom
• The top-left pixel should be black (0, 0, 0)
• The bottom-right pixel should be yellow (255, 255, 0)
• Print a valid PPM header: "P3", width, height, and max value 255
• Print each pixel's RGB values separated by spaces, with one pixel per line for readability
• Also print a simple ASCII preview using '#' for bright pixels and '.' for dark pixels
• Include a comment in the output explaining the PPM format