fix: Windows PowerShell 5.1 start_docker crash and paste-safe docs snippets

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/start_docker.ps1

@@ -7,7 +7,12 @@ $Utf8NoBom = [System.Text.UTF8Encoding]::new($false)
 
 function New-HexSecret {
     $bytes = [byte[]]::new(32)
-    [System.Security.Cryptography.RandomNumberGenerator]::Fill($bytes)
+    $rng = [System.Security.Cryptography.RandomNumberGenerator]::Create()
+    try {
+        $rng.GetBytes($bytes)
+    } finally {
+        $rng.Dispose()
+    }
     return -join ($bytes | ForEach-Object { $_.ToString('x2') })
 }