docs+nix: fix stale peer-hives-dashboard references (hyperhive#3294)

Follow-up to the peer-hives removal: docs/web-ui/dashboard.md drops
the whole "P33R H1V3S" section + its stale #peers hash and tab-strip
mentions; docs/swarm/README.md's runtime-effects list and
cross-references point at swarm-ui's roster page instead. Nix comments
in hive-c0re/environment.nix, swarm.nix and swarm-wireguard.nix that
described HYPERHIVE_PEERS/certFingerprint as dashboard-consumed are
updated to say what's actually still true (agent identity only).

Deliberately NOT removed: the `certFingerprint` nix option itself.
It has no remaining Rust consumer, but deleting a documented,
potentially already-set option is a bigger, breaking change than
removing dead display code — flagged in docs/swarm/README.md with a
note instead of silently dropped, so an operator or reviewer can make
that call explicitly rather than have it made for them here.

docs/swarm/README.md

@@ -129,10 +129,17 @@ conventionally `<name>.<swarm.domain>`, but a wrong domain that
 evaluates cleanly points at a real machine that isn't the one you meant.
 
 **`certFingerprint`** (`"sha256:…"`, optional) pins that hive's TLS
-_leaf_. Scopes **only** to hive-c0re's own peer HTTPS checks (the P33RS
-dashboard links + agent peer discovery below); matrix federation never
-consults it. Omit it for any hive under the swarm root CA or a public
-CA — which is the normal case.
+_leaf_. Matrix federation never consults it. Omit it for any hive
+under the swarm root CA or a public CA — which is the normal case.
+
+⚠️ **Currently unconsumed by any Rust code.** It was read by the
+per-hive dashboard's now-removed "peer hives" display (see below);
+that was its only consumer. Left in place rather than deleted along
+with that display — removing a documented, potentially
+already-set nix option is a bigger, more consequential (breaking)
+change than removing dead display code, and wants its own explicit
+decision rather than being swept up here. A future peer-facing
+feature (e.g. pinning a peer in `swarm-ui`) could pick it back up.
 
 > **There is no per-hive CA field.** Trust inside a swarm comes from the
 > swarm root ([`ca.md`](ca.md)): every hive chains to it, so one anchor
@@ -180,19 +187,17 @@ environment and forwarded to agent containers.
 
 ## What the config does at runtime
 
-1. **Dashboard P33RS tab** — hive-c0re reads `HYPERHIVE_PEERS` and
-   surfaces it as the peer list in the dashboard's state API. The
-   dashboard shows a P33RS tab (hidden when the list is empty) with a
-   card per peer linking to `https://{domain}/`. Wire format + module
-   pointer: `docs/web-ui/dashboard.md` § P33RS tab.
-
-2. **Agent identity** — the same `HYPERHIVE_PEERS` env var is
-   forwarded to agent containers, so agent code can discover peer
-   hives and address them with qualified names (`agent@domain`). See
+1. **Agent identity** — the `HYPERHIVE_PEERS` env var is forwarded to
+   agent containers, so agent code can discover peer hives and
+   address them with qualified names (`agent@domain`). See
    `hive-agent/src/identity.rs`'s module doc for the label/domain
-   helpers.
+   helpers. The swarm-wide hive roster used to also be shown as a
+   "peer hives" list on the per-hive dashboard; that display was
+   removed in favour of `swarm-ui`'s own roster page (`docs/swarm/
+   ui.md`), which reads the same directory from `swarm-controller`
+   instead.
 
-3. **Matrix federation** — when `matrix.enable` is on, tuwunel
+2. **Matrix federation** — when `matrix.enable` is on, tuwunel
    federates with the peer's matrix server (discovered via the peer's
    `.well-known/matrix/server` delegation, which the gateway serves).
    Federation validates the peer's TLS certificate against the matrix
@@ -370,6 +375,8 @@ it is stored in the queue, not in the daemon.
 - `docs/conventions.md` § Hive identity — env vars, qualified labels
 - `docs/matrix.md` — matrix federation, TLS cert auto-generation,
   firewall posture
-- `docs/web-ui/dashboard.md` § P33RS tab — dashboard surface
+- `docs/swarm/ui.md` — the swarm-wide hive roster, now the operator
+  surface for "what hives exist" (superseded the per-hive dashboard's
+  old "peer hives" display)
 - `docs/gateway.md` — nginx vhosts and the `.well-known/matrix/`
   auto-discovery scheme