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>

README.md

@@ -30,7 +30,6 @@ See the full table in [`containers/index.md`](containers/index.md). Quick links:
 | 121 | [caddy](containers/121-caddy.md)                   | 192.168.8.175 | Reverse proxy                                 |
 | 122 | [arriman](containers/122-arriman.md)               | 192.168.8.132 | Docker host (\*arr stack)                     |
 | 124 | [authentik](containers/124-authentik.md)           | 192.168.8.180 | SSO + split-horizon DNS                       |
-| 126 | [plato](containers/126-plato.md)                   | 192.168.8.190 | Plato (notes/discovery workspace)             |
 
 ### Cross-cutting infrastructure
 - [DNS — split-horizon](infrastructure/dns.md)