refactor(errors): defer mutation errors to global handler

Now that MutationCache toasts via toUserMessage by default, the per-hook
onError duplicates drop away. Also normalizes inline query-error UI and
surfaces a previously-silent failure.

Mutations — removed redundant onError toasts:
- network-selector: useAcceptInvitation, createNetwork (inline)
- network-settings: useInviteMembers, useRevokeInvitation, useRemoveMember
- network-billing: useCreateCheckoutSession, useCreatePortalSession
  (onSuccess toasts stay — they carry domain context like network name)

Queries — consistent inline error UX via toUserMessage:
- network-selector: failed-to-load state gets a "Try again" button
- network-billing: "Couldn't load billing" includes friendly reason
- network-settings: useNetworkInvitations failure now surfaces a hint
  (previously rendered as "0 pending" — silently wrong)

Trimmed noisy JSDoc from PR 1 files (errors.ts, query-client.ts,
app-error-boundary.tsx, error-fallback.tsx, ipc-utils.ts).

js/src/features/network-settings.tsx

@@ -79,9 +79,6 @@ function InviteForm({ networkId }: { networkId: string }) {
         toast.success(`Invitation sent to ${trimmed}`);
         setEmail("");
       },
-      onError: (err) => {
-        toast.error(err.message || "Failed to send invitation");
-      },
     });
   };
 
@@ -119,9 +116,6 @@ function PendingInvitationRow({
       onSuccess: () => {
         toast.success(`Invitation to ${email} revoked`);
       },
-      onError: (err) => {
-        toast.error(err.message || "Failed to revoke invitation");
-      },
     });
   };
 
@@ -188,7 +182,7 @@ export default function NetworkSettingsPage() {
   const [searchParams] = useSearchParams();
   const { data: networks } = useNetworks();
   const network = networks?.find((n) => n.id === networkId);
-  const { data: invitations } = useNetworkInvitations(networkId!);
+  const { data: invitations, error: invitationsError } = useNetworkInvitations(networkId!);
   const currentUser = useAuthStore((s) => s.user);
   const isAdmin = currentUser?.id === network?.admin_human.id;
   const [memberToRemove, setMemberToRemove] = useState<Human | null>(null);
@@ -286,6 +280,14 @@ export default function NetworkSettingsPage() {
             />
             <Separator />
             <InviteForm networkId={networkId!} />
+            {invitationsError && (
+              <>
+                <Separator />
+                <p className="text-muted-foreground px-4 py-3 text-xs">
+                  Couldn't load pending invitations.
+                </p>
+              </>
+            )}
             {pendingCount > 0 && (
               <>
                 <Separator />
@@ -354,9 +356,6 @@ export default function NetworkSettingsPage() {
                 toast.success(`Removed ${target.email}`);
                 setMemberToRemove(null);
               },
-              onError: (err) => {
-                toast.error(err.message || "Failed to remove member");
-              },
             });
           }}
           onClose={() => {