Unseenkey: download ældre versioner

Security fixes for every earlier version: a handle could send the real key to another host through a
crafted wildcard host, a Supabase or Jira key could go to a stranger's project, `..` got past policies,
and a failed key test could show the key. After updating, run `usk daemon restart`. Existing Supabase
and Jira keys need their own host named once. Also: Google service account keys, two-part keys such as
Twilio, seven new providers, `usk passwd`, and one-command setup with `usk mcp install`.
Not yet externally audited; installer not code-signed.