Added Race 2: tailscaled starts before network-online.target, causing
Tailscale to get stuck with SetNetworkUp(false). Covers both Ubuntu
ssh.socket and cross-platform tailscaled ordering issues. Updated
references to include majordiscord incident and new Ansible playbook.
Documents the systemd socket activation race where ssh.socket binds
to the Tailscale IP before tailscaled is ready, causing SSH to become
unreachable after a Tailscale reconnect. Includes diagnosis steps and
the After=/BindsTo= fix.