docs(windows): derive App Installer architecture from the environment

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X95PpvsxLn7q5S54kTPYhY

Author: claude

website/docs/installation/windows.mdx

@@ -60,11 +60,10 @@ without any interaction needed.
 Open a PowerShell prompt and run the following command:
 
 ```powershell
-Add-AppxPackage -AppInstallerFile https://cdn.ohmyposh.dev/releases/latest/install-x64.appinstaller
+$arch = if ([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture -eq 'Arm64') { 'arm64' } else { 'x64' }
+Add-AppxPackage -AppInstallerFile "https://cdn.ohmyposh.dev/releases/latest/install-$arch.appinstaller"
 ```
 
-For ARM64, use `install-arm64.appinstaller` instead.
-
 </TabItem>
 <TabItem value="chocolatey">
 
@@ -111,7 +110,8 @@ No action needed, Windows updates Oh My Posh automatically in the background.
 To force an update check, run the install command again:
 
 ```powershell
-Add-AppxPackage -AppInstallerFile https://cdn.ohmyposh.dev/releases/latest/install-x64.appinstaller
+$arch = if ([System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture -eq 'Arm64') { 'arm64' } else { 'x64' }
+Add-AppxPackage -AppInstallerFile "https://cdn.ohmyposh.dev/releases/latest/install-$arch.appinstaller"
 ```
 
 </TabItem>