format_bytes_for_user prints KB/MB/GB for base-1024 math

Problem

format_bytes_for_user (apps/rocm/src/main.rs) divides by 1024 but labels the result KB, MB, GB. The units say base 1000; the arithmetic is base 1024, so every figure it prints is mislabelled.

format_bytes, used by rocm storage, does the same arithmetic and prints KiB, MiB, GiB. Two size formatters with the same maths and different units now both appear in user-facing output.

Suggested direction

Pick one and use it everywhere: either correct the units on format_bytes_for_user to the Ki/Mi/Gi forms, or make it genuinely base 1000. Then collapse the two functions so there is a single size formatter.

Context

Out of scope for #172, which only made format_bytes live and fixed its rounding at unit boundaries. format_bytes_for_user reaches unrelated call sites, so changing its output belongs in its own change. Raised from review feedback on that PR.

Start in apps/rocm/src/main.rs by reading format_bytes_for_user and format_bytes, then trace their user-facing call sites. Choose one unit convention and consolidate the two formatters without changing the scope of #172. Done means both paths use one formatter with arithmetic and labels that agree.