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/darts.md

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+# darts
+
+An opaque third-party/customer VM. Declared in `colony`'s `my.vms.instances`
+but **not a NixOS system**: this repo knows nothing about what runs inside it
+and doesn't manage it.
+
+- **Source (host-side only):** the `darts` instance in
+  [`nixos/boxes/colony/vms/default.nix`](../../../nixos/boxes/colony/vms/default.nix)
+  and the `90-vm-darts` network in
+  [`nixos/boxes/colony/default.nix`](../../../nixos/boxes/colony/default.nix)
+- **Host:** VM on `colony`
+- **nixpkgs:** not applicable (unmanaged guest; host-side definition uses `colony`'s `mine-stable`)
+
+## Role
+
+- Customer/dedicated VM, left alone beyond hosting and connectivity.
+- A thin-provisioned `root` LV on the NVMe pool, plus `darts-media` (RAID 5 across the four HDDs)
+  and `darts-ext` (linear storage on the 18 TB HDD) in the `main` VG. See
+  [`colony`'s storage layout](colony.md#storage).
+
+## Network assignments
+
+This guest is not a NixOS system, so its host-routed addresses are not rows in the generated
+[network assignments](../../networking.md#box-assignments) table.
+
+- Same customer-VM pattern as [`mail`](mail.md): dedicated unbridged TAP
+  (`vm-darts`), point-to-point address
+  (`custRouting.darts-vm`) on the host side, link-routed public /32
+  `94.142.242.255`, and the IPv6 /64 `2a0e:97c0:4d2:2001::/64` with RAs.
+- DNS: `darts-cust.ams1.int.nul.ie`. Like the other customer prefixes, its
+  inbound traffic is accepted by `estuary` without per-port filtering and
+  forwarded on by `colony`.
+
+## Notable config files
+
+- [`nixos/boxes/colony/vms/default.nix`](../../../nixos/boxes/colony/vms/default.nix) — VM definition.
+- [`nixos/boxes/colony/default.nix`](../../../nixos/boxes/colony/default.nix) — host-side network and routing.