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.

lib/constants.nix

@@ -318,7 +318,7 @@ rec {
       # the switches to river (PPPoE runs directly on it), and the switch at the ONT edge PVIDs the
       # untagged management port onto wan-pon-ont (140). wan-pon-isp (141) is reserved for the
       # future multi-ONT case, where per-port VLAN translation on a dedicated switch swaps each
-      # ONT's VLAN 10 to a distinct fabric VLAN (see home-switches.md).
+      # ONT's VLAN 10 to a distinct fabric VLAN (see docs/sites/home/switches.md).
       pon-isp = 10;
       wan-pon-ont = 140;
       wan-pon-isp = 141;