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/colony-psql.md

@@ -0,0 +1,43 @@
+# colony-psql
+
+The shared PostgreSQL instance for colony services. Rather than each service running its own
+database, the containers (and the `git` VM) connect here over the `ctrs` network.
+
+- **Source:** [`shill/containers/colony-psql.nix`](../../../../../nixos/boxes/colony/vms/shill/containers/colony-psql.nix)
+- **Host:** NixOS container on [`shill`](../../shill.md)
+
+## Role
+
+- **PostgreSQL 14** with TCP/IP enabled, reachable from the whole colony (`10.100.0.0/16` and
+  `2a0e:97c0:4d2:10::/60`, `md5` auth). The firewall allows `5432`.
+- Local `peer` auth maps `postgres`, `root`, `netdata` and `dev` to the `postgres` superuser via
+  the ident map.
+- **netdata** with the Python PostgreSQL collector.
+- Consumers wait for the database to accept connections with the `lib.my.systemdAwaitPostgres`
+  helper (e.g. `sharry`, `atticd`, `mastodon-init-db`, and `middleman`'s nginx as a DNS
+  bootstrap hack).
+
+## Network assignments
+
+<!-- assignments: colony-psql -->
+<!-- assignments-start -->
+| Name | Assignment | IPv4 | IPv6 | Domain | Notes |
+|---|---|---|---|---|---|
+| colony-psql-ctr (colony-psql) | internal | `10.100.2.4/24 gw 10.100.2.1` | `2a0e:97c0:4d2:12::4/64` | ams1.int.nul.ie |  |
+<!-- assignments-end -->
+
+The assignment also has the alt name `colony-psql` (no `-ctr` suffix), which is what consumers
+use as the database hostname.
+
+## Consumers
+
+- [object](object.md) — `sharry` and `hedgedoc` (and `atticd` when enabled) over
+  `colony-psql:5432`
+- [toot](toot.md) — Mastodon's database (Mastodon currently disabled)
+- [chatterbox](chatterbox.md) — the mautrix bridges (WhatsApp, Messenger, Instagram) via
+  Postgres URIs in their secret env files
+- `git` VM — Gitea
+
+## Notable config files
+
+- [`nixos/boxes/colony/vms/shill/containers/colony-psql.nix`](../../../../../nixos/boxes/colony/vms/shill/containers/colony-psql.nix) — container definition and PostgreSQL configuration