nx_paint_fb_ascii_dump_test.nx

nx_paint_fb_ascii_dump_test.nx -- smoke for ASCII-art framebuffer dump. Builds a small framebuffer with a known-color rectangle, dumps it, verifies the exact byte pattern. Fixture: 4x3 framebuffer cleared to zero, fill 2x1 red rect at (1, 1). Expected: row 0: " \n" (all transparent) row 1: " ## \n" (red pixels at x=1,2 -> '#') row 2: " \n" Total = 5 chars per row * 3 rows = 15 bytes.