fix(select_device.ps1): make DTB/logo update atomic with rollback

[bhoot1234567890]

Problem

select_device.ps1 updates the boot partition's DTB + logo files with a delete-then-copy sequence:

Get-ChildItem $rootDir -Filter "*.dtb" | ForEach-Object { Remove-Item $_.FullName -Force }   # delete all .dtb
Remove-Item $oldLogo -Force                                                                  # delete logo
Copy-Item "$sourceFolder\*" -Destination $rootDir ...                                        # then copy
Copy-Item $logoSrc -Destination logo.bmp ...

If the copy fails partway — disk full, card pulled mid-write, unreadable source, or a locked file — the boot partition is left with no DTB files and the device won't boot. For a tool whose whole purpose is keeping the handheld bootable, that's the one gap worth closing.

Fix

Make the apply step atomic with rollback:

1. Stage the incoming .dtb + logo into a temp dir first — a bad/unreadable source fails here, before anything on the boot volume is touched.
2. Back up the current root .dtb files and logo.bmp.
3. Install the staged files into root.
4. Only then remove the superseded old .dtb files.

Wrapped in try/catch: on any failure the backup is restored so the device returns to its prior bootable state, then the script exits non-zero. The rollback is best-effort per file (a single locked/unwritable file can't abort it) and also discards any new files the failed install partially wrote, so root ends up matching its pre-update state. Temp dirs are cleaned up on both success and failure paths.

Scope

Only the "Apply changes" section. No change to INI parsing, the menu, or device-selection logic. Behaviour is identical on the happy path; only the failure mode changes (safe rollback instead of a bricked partition).

Testing

Parsed clean with the PowerShell AST parser, then ran the extracted apply block against a mock filesystem on PowerShell 7.6:

Scenario	Result
Happy path	new DTBs installed, superseded files removed, logo updated, temp dirs cleaned, exit 0
Empty source folder	fails at stage before touching root, exit 1, root untouched
Partial install failure (dest unwritable mid-copy)	rollback restores exact prior file set, discards leftover new files, exit 1