decommission: destroy plato (LXC 126)

LXC 126 stopped and destroyed on hubris. Remove all live references:
inventory, container doc, host file, README, containers index, auto-deploy
pipeline, DNS entry, SSH access table, nfs-export mount list.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/plato.yaml

@@ -1,28 +0,0 @@
-# Generated by mcp/build_host_files.py from inventory.yaml.
-# Do NOT edit by hand — your changes will be overwritten.
-# Source of truth: ../inventory.yaml
-name: plato
-kind: lxc
-os: linux
-role: app
-host: hubris
-pve_id: 126
-lan_ip: 192.168.8.190
-mesh_globals:
-  primary: netbird
-  accepted:
-  - netbird
-  - tailscale
-mounts:
-- /mnt/library/documents/plato
-public_host: plato.hubris.network
-runs:
-- plato
-services_hosted:
-- name: plato
-  url: https://plato.hubris.network
-  backend: plato
-see_also:
-- containers/126-plato.md
-mcp_endpoint: https://mcp.hubris.network/mcp
-secrets_issuance_endpoint: https://secrets.hubris.network/issue