feat(webi): probe zst as unpacker; properly probe formats in webi-pwsh

webi/webi.sh: detect unzstd/zstd alongside the existing git/unxz/
unzip/tar probes. Sends `?formats=...,zst` when zstd is available so
the server can pick a .tar.zst build only on hosts that can extract
it.

webi/webi-pwsh.ps1: replace the hardcoded `formats=zip,exe,tar,git`
TODO with real Get-Command probing for git, zstd, and 7z.

webi/webi-pwsh.ps1

@@ -194,8 +194,11 @@ Write-Host "${TTask}Installing${TReset} ${TName}${exename}${TReset}"
 Write-Host "    ${TDim}Fetching install script ...${TReset}"
 
 $PKG_URL = "$Env:WEBI_HOST/api/installers/$exename.ps1"
-# TODO detect formats
-$UrlParams = "formats=zip,exe,tar,git&libc=msvc"
+$DetectedFormats = @("zip", "exe", "tar")
+if (Get-Command git -ErrorAction SilentlyContinue) { $DetectedFormats += "git" }
+if (Get-Command zstd -ErrorAction SilentlyContinue) { $DetectedFormats += "zst" }
+if (Get-Command 7z -ErrorAction SilentlyContinue) { $DetectedFormats += "7z" }
+$UrlParams = "formats=$($DetectedFormats -join ',')&libc=msvc"
 $PkgInstallPwsh = "$HOME\.local\tmp\$exename.install.ps1"
 Invoke-DownloadUrl -Force -URL $PKG_URL -Params $UrlParams -Path $PkgInstallPwsh
 

webi/webi.sh

@@ -40,6 +40,9 @@ __webi_main() {
     if [ -n "$(command -v git)" ]; then
         my_ext="git,$my_ext"
     fi
+    if [ -n "$(command -v unzstd)" ] || [ -n "$(command -v zstd)" ]; then
+        my_ext="zst,$my_ext"
+    fi
     if [ -n "$(command -v unxz)" ]; then
         my_ext="xz,$my_ext"
     fi