fix: improve wheel download script reliability

scripts/install_offline.ps1

@@ -1,5 +1,6 @@
 param(
-  [switch]$NoPause
+  [switch]$NoPause,
+  [string]$IndexUrl = "https://pypi.org/simple"
 )
 
 $ErrorActionPreference = "Stop"
@@ -130,11 +131,18 @@ function Install-Requirements {
     & $VenvPython -m pip install --no-index --find-links $WheelDir -r $Req
   } else {
     Write-Host "No offline wheels found. Installing dependencies from the network."
-    & $VenvPython -m pip install -r $Req
+    & $VenvPython -m pip install `
+      --index-url $IndexUrl `
+      --trusted-host pypi.org `
+      --trusted-host files.pythonhosted.org `
+      --disable-pip-version-check `
+      --retries 3 `
+      --timeout 60 `
+      -r $Req
   }
 
   if ($LASTEXITCODE -ne 0) {
-    throw "Dependency installation failed. If the server is offline, run scripts\download_wheels.ps1 on an online machine first and copy vendor\wheels to this server."
+    throw "Dependency installation failed. Check network access to $IndexUrl. If the server is offline, run scripts\download_wheels.ps1 on an online machine first and copy vendor\wheels to this server."
   }
 }