fix(shard): stop an undecryptable uo-link token 500ing every live-shard route

`uoLinkClient.call()` resolved the uo-link config OUTSIDE its try/catch.
resolveConfig() decrypts the stored auth token, and secretBox.decrypt throws
when the ciphertext can't be authenticated — SECRET_ENC_KEY rotated, or a DB
dump restored into an environment keyed differently. That throw escaped the
client entirely, breaking its documented "never throws / always returns
{ ok, data, status }" contract and turning a misconfiguration into a 500 on
every route that does a live sidecar round-trip:

  GET /admin/uo-link/config
  GET /{admin,player}/shard/char/:serial
  GET /{admin,player}/shard/roster/:account
  GET /{admin,player}/shard/vendors/:account

Found by a live smoke test of all 200 routes at every access level. Public
shard routes were unaffected because they read the DB via getSafe(), which
never decrypts.

Move resolveConfig() inside the try so the failure returns the standard
{ ok: false } shape, and log it at ERROR with a distinct message: a wrong key
previously looked identical to "the shard is offline", with no clue why.
Those routes now degrade to 503, and GET /admin/uo-link/config returns 200
again — it is the screen an admin needs to re-enter the token and recover, so
having it 500 locked them out of the fix.

Also gate the admin Dashboard's site-mode toggle. PUT /admin/site-mode is
adminOnly, but the button rendered for every staff role, and toggle() had a
try/finally with no catch — so an editor clicking it got an unhandled promise
rejection and zero UI feedback. Gate the control on role === 'admin' (the rule
AdminLayout already documents: never show a non-admin a control that would 403)
and surface a message if the call is refused anyway.

Adds server/test/uoLinkClient.test.js, which fails against the unfixed client.

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

client/src/routes/admin/views/Dashboard.jsx

@@ -4,9 +4,15 @@ import { useAsync } from '../../../lib/useAsync.js'
 import { ago, dateTime } from '../../../lib/format.js'
 import { api } from '../../../api/client.js'
 import { useSite } from '../../../contexts/SiteContext.jsx'
+import { useAuth } from '../../../contexts/AuthContext.jsx'
 
 export default function Dashboard() {
   const { refresh: refreshSite } = useSite()
+  const { user } = useAuth()
+  // PUT /admin/site-mode is adminOnly. The dashboard itself is staff-wide, so the
+  // toggle needs its own gate — same rule the sidebar follows (AdminLayout: never
+  // show a non-admin a control that would 403).
+  const isAdmin = user?.role === 'admin'
   const [tick, setTick] = useState(0)
   const reload = useCallback(() => setTick((t) => t + 1), [])
 
@@ -15,6 +21,7 @@ export default function Dashboard() {
     [tick],
   )
   const [busy, setBusy] = useState(false)
+  const [modeError, setModeError] = useState('')
 
   if (loading) return <Loading />
   if (error) return <ErrorState message="Could not load the dashboard." />
@@ -32,12 +39,21 @@ export default function Dashboard() {
     { value: dash.counts?.users ?? 0, label: 'Users' },
   ]
 
+  // The rejection was previously unhandled: a refused toggle surfaced only as an
+  // unhandled promise rejection in the console while the button silently reverted.
   async function toggle() {
     setBusy(true)
+    setModeError('')
     try {
       await api.admin.setSiteMode(isLive ? 'maintenance' : 'live')
       await refreshSite()
       reload()
+    } catch (err) {
+      setModeError(
+        err.status === 403
+          ? 'Only an administrator can change the site mode.'
+          : 'Could not change the site mode. Try again.',
+      )
     } finally {
       setBusy(false)
     }
@@ -78,15 +94,22 @@ export default function Dashboard() {
             {changed.by ? `Changed by ${changed.by}` : 'No changes recorded'}
             {changed.at ? ` · ${dateTime(changed.at)}` : ''}
           </div>
+          {modeError && (
+            <div className="sans" style={{ fontSize: '0.8rem', marginTop: 8, color: 'var(--danger, #d98b8b)' }}>
+              {modeError}
+            </div>
+          )}
         </div>
-        <button
-          onClick={toggle}
-          disabled={busy}
-          className="sans"
-          style={{ border: '1px solid var(--accent)', borderRadius: 999, padding: '11px 24px', background: 'rgba(127,153,189,0.14)', color: '#d8e2ef', fontWeight: 600, fontSize: '0.9rem', cursor: 'pointer' }}
-        >
-          {modeLabel}
-        </button>
+        {isAdmin && (
+          <button
+            onClick={toggle}
+            disabled={busy}
+            className="sans"
+            style={{ border: '1px solid var(--accent)', borderRadius: 999, padding: '11px 24px', background: 'rgba(127,153,189,0.14)', color: '#d8e2ef', fontWeight: 600, fontSize: '0.9rem', cursor: 'pointer' }}
+          >
+            {modeLabel}
+          </button>
+        )}
       </div>
 
       <div className="grid-4" style={{ gap: 14, marginBottom: 28 }}>