fix: federated space icon display/upload in settings, restyle settings panels

Fix three federation bugs in Space Settings: icon URL was double-wrapped
through home API, upload targeted home instance instead of remote, and
updateSpace used home API client. Also restyle settings panels (User,
Space, Members, Roles, Connected Instances) with consistent section
headers, grouped cards, and improved layout.

packages/web/src/components/modals/ConnectedInstances.tsx

@@ -381,12 +381,13 @@ export function ConnectedInstances() {
   const [showAddForm, setShowAddForm] = useState(false);
 
   return (
-    <div className="border-t border-white/[0.06] pt-4">
-      <h3 className="text-xs font-bold text-txt-secondary uppercase mb-3">
+    <div>
+      <div className="text-[11px] font-semibold text-txt-tertiary uppercase tracking-wider mb-1.5">
         Connected Instances
-      </h3>
+      </div>
+      <p className="text-xs text-txt-tertiary mb-2">Link accounts across federated Backspace instances.</p>
 
-      <div className="space-y-2">
+      <div className="rounded-lg bg-white/[0.02] p-3 space-y-2">
         {/* Home instance (always shown, non-removable) */}
         <div className="flex items-center justify-between p-3 bg-surface-channel rounded-lg">
           <div className="flex items-center gap-2 min-w-0">