docs: Document the deployment

Add a top-level README mapping the boxes and a full docs/ tree: topic
pages (architecture, networking, deployment), per-site box pages for
colony and home with containers nested under their hosts, remote and
mobile boxes, the installer, and the home switch fabric reference
(folded in from home-switches.md, with AGENTS.md and code comments
retargeted to its new home). Box pages carry marked assignment tables
that CI regenerates from nixos.allAssignments.

AGENTS.md points at the new docs and keeps its terse agent version of
the mechanics, referring to the topic pages for depth.

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

@@ -0,0 +1,27 @@
+# gam
+
+A game-server container — the lightweight counterpart to the OCI game servers on `whale2`,
+running servers directly as NixOS services. Currently it runs a single Terraria server.
+
+- **Source:** [`shill/containers/gam.nix`](../../../../../nixos/boxes/colony/vms/shill/containers/gam.nix)
+- **Host:** NixOS container on [`shill`](../../shill.md)
+
+## Role
+
+- **terraria** — dedicated server (`services.terraria`): world at
+  `/var/lib/terraria/NotWorld.wld`, auto-created large worlds, MOTD "sup gamers", UPnP off.
+  Extra settings (e.g. password) come from the `gam/terraria.conf` age secret used as the config
+  file. `openFirewall` is on, and `estuary` port-forwards TCP and UDP `7777` to this container.
+
+## Network assignments
+
+<!-- assignments: gam -->
+<!-- assignments-start -->
+| Name | Assignment | IPv4 | IPv6 | Domain | Notes |
+|---|---|---|---|---|---|
+| gam-ctr | internal | `10.100.2.11/24 gw 10.100.2.1` | `2a0e:97c0:4d2:12::b/64` | ams1.int.nul.ie |  |
+<!-- assignments-end -->
+
+## 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