docs(3167): the setup guide gains a swarm UI step, and one group name

Per mara on the PR: the guide someone follows on a fresh deploy is a
different page from the one they read while debugging, and only the
second existed.

Also fixes a contradiction the request surfaced: setup.md and
swarm/sso.md have told every operator to create '--group admins' since
the bootstrap step existed, while the new rule required 'operators'.
This is the first rule that CONSUMES a group name, so it takes the one
the guide already creates - inventing a second would have meant every
account made by following the guide silently failing the check it was
supposed to pass, and for mara specifically a migration step that now
may not be needed at all.

setup.md's step 3 says why --group is not decoration; the new step 4
says what decides whether the page opens (the group, and the name
resolving) rather than listing a command, because there is nothing to
run. Steps renumbered, including the matrix block's internal 4a-4e.

docs/setup.md

@@ -49,30 +49,51 @@ start. Skipping this step looks like a broken proxy.
 swarmctl user add mara --display-name Mara --email mara@example.com --group admins
 ```
 
+⚠️ **Keep `--group admins`.** It is not decoration: operator-only
+surfaces (the swarm UI below) are gated on that group, and an account
+without it authenticates successfully and is then refused — which reads
+like a broken login rather than a missing group.
+
 Detail, including what the password is and why this stays manual:
 [`swarm/sso.md`](swarm/sso.md).
 
-### 4 · Matrix
+### 4 · Swarm UI (only when `swarm.ui.enable`, on by default with the controller)
+
+Nothing to run — it is served on the swarm apex
+(`https://<swarm.domain>/`) as soon as the host rebuilds. Two things
+decide whether you can actually open it:
+
+- **You are in `admins`** (step 3). The gateway asks authelia whether
+  you have a session; the rule that makes it mean *operator* wants the
+  group. Without it you log in and still get bounced.
+- **The name resolves to this host.** It is published to the hive's own
+  resolver and to `/etc/hosts` when `gateway.localHostsEntry` is on; from
+  anywhere else it needs a real DNS record like any other public name.
+
+Detail, including why reachability is deliberately not the access
+control: [`swarm/ui.md`](swarm/ui.md).
+
+### 5 · Matrix
 
 ```bash
-# 4a. Ensure the hive-internal admin account exists first
+# 5a. Ensure the hive-internal admin account exists first
 hivectl matrix sync-admin
 
-# 4b. Provision ruth's own matrix account
+# 5b. Provision ruth's own matrix account
 hivectl matrix create-user ruth
 
-# 4c. Create a human matrix account
+# 5c. Create a human matrix account
 hivectl matrix create-user mara --password hunter2
 
-# 4d. Invite the operator to the hive Space (and optionally to rooms)
+# 5d. Invite the operator to the hive Space (and optionally to rooms)
 hivectl matrix invite mara
 hivectl matrix invite @mara:yourserver --room '#hive-chat:yourserver'
 
-# 4e. Promote the operator to homeserver admin if needed
+# 5e. Promote the operator to homeserver admin if needed
 hivectl matrix promote-user mara
 ```
 
-### 5 · Spawn sub-agents
+### 6 · Spawn sub-agents
 
 Sub-agent creation goes through the approval queue — ruth proposes, the
 operator approves, the container builds. From ruth's own turn (inside
@@ -93,7 +114,7 @@ request_init_config(name: "iris")
 
 See [`approvals.md`](approvals.md) for the full flow.
 
-### 6 · Useful host commands
+### 7 · Useful host commands
 
 ```bash
 # Roster: all agents, status, rev, parent, pending reminders

docs/swarm/README.md

@@ -97,7 +97,7 @@ another container, and the three ways that one gets delivered:
 ## Swarm UI
 
 The operator-only web surface on the swarm apex, why reaching it needs
-the `operators` group rather than just a session, and the four sites a
+the `admins` group rather than just a session, and the four sites a
 swarm service name has to be wired into: [`ui.md`](ui.md).
 
 ## The swarm's hive directory

docs/swarm/ui.md

@@ -25,21 +25,28 @@ way `swarm.forge.domain` and `swarm.matrix.gatewayHost` can.
 > claiming one `server_name` do not error — nginx picks one — so this is
 > an assertion rather than a runtime surprise.
 
-## 🔑 You must be in the `operators` group
+## 🔑 You must be in the `admins` group
 
 **This is the step that separates "protected" from "locked out".** The
 vhost's `auth_request` asks authelia *"is there a session"*; the rule
 that makes it mean *"is this an operator"* is an `access_control` entry
-requiring `group:operators`. An account without that group authenticates
+requiring `group:admins`. An account without that group authenticates
 fine and still gets bounced.
 
 ```sh
-swarmctl user add <you> --group operators
+swarmctl user add <you> --group admins
 ```
 
-An account created before this existed has no groups. Re-add it with the
-flag — `swarmctl` treats an existing entry as the canonical store, so the
-group is what changes.
+`admins` deliberately, not a new word: [`../setup.md`](../setup.md) has
+told every operator to create exactly that group since the bootstrap step
+existed, so an account made by following the guide already passes. This
+is the first rule that *consumes* a group name — inventing a second one
+would have meant those accounts silently failing a check they were
+supposed to pass.
+
+An account created without any group needs re-adding with the flag —
+`swarmctl` treats the existing entry as the canonical store, so the group
+is what changes.
 
 Why a group and not a list of usernames: agents are getting authelia
 accounts of their own (matrix SSO), and *authenticated* would then

nix/host-modules/swarm-authelia.nix

@@ -43,7 +43,14 @@ let
   # here because this module writes the rule that enforces it and
   # `swarmctl user add --group <this>` is what grants it — the two must
   # agree, and one constant is how they stay agreeing.
-  operatorGroup = "operators";
+  #
+  # ⚠️ `admins` and not a new word, because `docs/setup.md` and
+  # `docs/swarm/sso.md` have been telling every operator to create
+  # exactly that group since the bootstrap step existed. This is the
+  # first rule that CONSUMES a group name; picking a different one would
+  # have meant every account created by following the guide silently
+  # failing the check it was supposed to pass.
+  operatorGroup = "admins";
 
   # Upstream's `services.authelia.instances.<name>` derives the unit,
   # user, group and StateDirectory from the instance name