docs/boxes: Document deployed boxes

Add per-site and per-box inventories, consolidate shared network design,
and relocate the switch and access-point references under the home site.

docs/sites/colony/shill/containers/gam.md

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+# gam
+
+A game-server container currently dedicated to Terraria.
+
+- **Source:** [`shill/containers/gam.nix`](../../../../../nixos/boxes/colony/vms/shill/containers/gam.nix)
+- **Host:** NixOS container on [`shill`](../README.md)
+- **nixpkgs:** `mine`
+
+## Role
+
+Runs lightweight game servers directly as NixOS services, rather than as OCI containers on
+[`whale2`](../../whale2.md).
+
+## Network assignments
+
+See the consolidated [network assignments](../../../../networking.md#box-assignments) table (this box: `gam`).
+
+## Terraria server
+
+`services.terraria` runs the dedicated server with its world at
+`/var/lib/terraria/NotWorld.wld`. It creates large worlds automatically, uses the MOTD
+"sup gamers", and disables UPnP. Additional settings such as the password come from the
+`gam/terraria.conf` age secret used as the service configuration file.
+
+`openFirewall` is enabled, and `estuary` forwards TCP and UDP port `7777` to the container.
+
+## Notable config files
+
+- [`nixos/boxes/colony/vms/shill/containers/gam.nix`](../../../../../nixos/boxes/colony/vms/shill/containers/gam.nix) — container definition and the Terraria service