feat: auto-install msitools in both SWBF2 setup scripts

Both scripts now detect and install msitools if missing, supporting
apt-get (Debian/Ubuntu), dnf (Fedora), and pacman (Arch). Falls back
to a clear error if the package manager is not recognised.

Remove msitools from manual prerequisites in the doc.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D8ckUJQtj1pH8jtAddBDZs

docs/SWBF2-2017-linux-setup.md

@@ -19,13 +19,9 @@ wrapper to import the necessary registry entries on every launch.
 ## Prerequisites (both setups)
 
 - SWBF2 (AppID 1237950) installed via Steam and fully downloaded
-- GE-Proton10-34 — the setup scripts install this automatically if not present
+- GE-Proton10-34 — installed automatically by the setup scripts if not present
+- `msitools` — installed automatically by the setup scripts if not present
 - An EA account created at ea.com and linked to your Steam account
-- `msitools` installed on the host:
-  ```bash
-  sudo apt-get install -y msitools     # Debian / Ubuntu
-  sudo dnf install -y msitools         # Fedora
-  ```
 
 ### EA account requirement