Fix Windows SD and USB reader flashing

[bestquark]

What changed

• make Windows disk preparation state-aware and idempotent
• support USB-A, USB-C, native SD, and MMC readers
• fall back to safely dismounting card volumes when a reader cannot offline the whole disk
• surface the actual PowerShell error instead of only the failed command
• add native Windows regression tests and package validation

Root cause

The helper always cleared read-only state and took the disk offline on both preparation passes. At 98.5%, many cards were already offline, and some Windows storage drivers reject a read-only update against an offline disk. Other removable-media drivers do not implement whole-disk offline state at all.

Validation

• make test
• Python USB/SD/MMC safety and command regression tests
• Windows Actions job exercises the PowerShell transitions and builds the packaged helper