fix: offer only what an install can do

Back from the systems list with nothing ticked keeps the ticks it
opened with, and None says First system once nothing is left to untick.
Confirm under --offline with nothing on hand has no Install, and the line
mode no longer asks to download what --offline never fetches. The line
mode counts the data files before its question.

Screen words: the checking clock starts at zero, a pack installs from
the pack, the copies found are said on a line of their own, the screen
of misplaced files says the copies stay, the save folder gets a line of
its own, the shared note is one line, a size keeps its unit, the same
save folder remedy on both screens, A Tick on the Miyoo bar, no Home
key in the help of a pad, and a system name said once with a pack.

install.ps1

@@ -11,7 +11,7 @@
 
     $ErrorActionPreference = "Stop"
     $defaultInstallUrl = "https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-    $defaultInstallSha256 = "8833256124ffdfa38865e7b065f2720ec20997e1a91ba340eab4067e31b20727"
+    $defaultInstallSha256 = "d59defaa5802d2d7b73b4b02e693e9592618803b308eb625a6f436b8a5388464"
     $maximumInstallerBytes = 2MB
     $installerExit = 0
     $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }