Decommission LXC 109 (syncthing)

Container had been stopped since 2026-04-21 and was never re-enabled.
pct destroy 109 --purge cleaned up vm-109-disk-0 on local-lvm and the
config file. /mnt/library/syncthing subtree was already empty at the
time of destruction and is retained as an empty dir (no real data to
migrate or back up).

- README.md, containers/index.md: removed row, moved to "recently
  destroyed" table
- hosts/hubris.md: dropped from /mnt/library subtree list, updated
  containers/index summary line, added changelog entry
- infrastructure/media-permissions.md: dropped from membership table
  and onboarding example, generalised pct-exec gotcha hostname,
  added changelog
- vms/100-zimaos.md: dropped from "existing fleet" enumeration
- containers/102-nfs-export.md: dropped from bind-mount sibling list
  (7 LXCs now, not 8)
- containers/109-syncthing.md: deleted

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -23,7 +23,6 @@ See the full table in [`containers/index.md`](containers/index.md). Quick links:
 | 103 | [paperless](containers/103-paperless.md)           | 192.168.8.130 | Document mgmt                                 |
 | 104 | [gitea](containers/104-gitea.md)                   | 192.168.8.121 | Git server                                    |
 | 105 | [apps](containers/105-apps.md)                     | 192.168.8.205 | Docker host (Artifacto / Booklore / PlantUML / Portainer / WriteFreely) |
-| 109 | [syncthing](containers/109-syncthing.md)           | (stopped)     | File sync                                     |
 | 114 | [nextcloud](containers/114-nextcloud.md)           | 192.168.8.224 | Personal cloud                                |
 | 118 | [elementsynapse](containers/118-elementsynapse.md) | 192.168.8.239 | Matrix Synapse                                |
 | 119 | [sophia](containers/119-sophia.md)                 | 192.168.8.157 | Sophia                                        |