docs: Document the boxes

Add a top-level `README.md` mapping the boxes and per-machine docs under
`docs/boxes/` (grouped `colony/`, `home/`, `misc/`), one file per host, VM and
container documenting role, services and networking with source pointers.

Also point `AGENTS.md` at the new docs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/boxes/colony/toot.md

@@ -0,0 +1,19 @@
+# toot
+
+A federated-social container. Despite the name (Mastodon = "toots"), it currently
+hosts a **Bluesky PDS**; the Mastodon instance is disabled.
+
+- **Source:** [`shill/containers/toot.nix`](../../../nixos/boxes/colony/vms/shill/containers/toot.nix)
+- **Host:** NixOS container on `shill`
+
+## Role
+
+- **Bluesky PDS** (Personal Data Server) — the active service, published as
+  `pds.nul.ie` (proxied by `middleman` to `:3000`).
+- **Mastodon** — **currently disabled**. The config is still present and
+  `toot.nul.ie` still maps to `:80`, but the instance is not running. (It was
+  backed by the shared `colony-psql` and MinIO/S3 on `object`.)
+
+## Networking
+
+- `internal` assignment on the `ctrs` network (alt name `toot-ctr`).