Give the nav's dead links somewhere to land

Three of the app's routes were referenced but never existed, so the redesign's
navigation pointed at 404s from several directions.

/dashboard was the post-login and fallback redirect target in nine places --
login, onboarding, middleware, the admin/nodes/systems/tokens/settings guards,
and the marketing header -- but app/dashboard/ was never created. Signing in
normally dropped the user on a 404. The real signed-in home is "/", which
app/page.tsx already renders as LiveView for an authed user with an org, and
which the nav labels "Live"; all nine now point there.

Nav also linked /watch and /network, neither of which existed. /watch is the
alerts screen under its redesign name, so it re-exports app/alerts/page.tsx
and /alerts stays reachable for old links. /network is new: the "my equipment"
hub the redesign moved /nodes, /systems and /tokens behind and then never
built, which had left /systems and /tokens with no entry point in the UI at
all. Its hooks all run before the admin/operator guard, per d041c86.

Separately, the admin page's guard read isAdmin without authLoading, so every
cold load of /admin -- typed URL, hard refresh, bookmark -- redirected away
while the Firebase claims were still resolving. Admin was only reachable by
clicking through from an already-mounted page. Now it waits, like every other
guarded route does.

And /incidents no longer lies about an empty list: a failed Firestore query
leaves `incidents` empty just as a quiet night does, and the page was printing
"No incidents recorded yet" over the top of a missing-composite-index error.
useIncidents already returned `error`; the page just ignored it. It now renders
an ErrorBanner instead, so the undeployed indexes in server-26#13 read as a
failure rather than as silence on the radio.

Closes server-26#30, server-26#31. server-26#13 stays open -- the rules and
indexes still have to be pushed to the live project by hand.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

drb-frontend/app/tokens/page.tsx

@@ -26,7 +26,7 @@ export default function TokensPage() {
   const [error, setError] = useState<string | null>(null);
 
   useEffect(() => {
-    if (!authLoading && !isAdmin && !isOperator) router.replace("/dashboard");
+    if (!authLoading && !isAdmin && !isOperator) router.replace("/");
   }, [authLoading, isAdmin, isOperator, router]);
 
   const refresh = useCallback(async () => {