fix: use SI decimal file size units

[naveensingh]

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

Updated formatSize() helpers to divide by 1000 instead of 1024.

Tests performed

• Confirmed file size in all apps that rely on formatSize()

Closes the following issue(s)

• Closes Allow to display file/storage sizes in decimal base General-Discussion#794

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• All checks are passing.