feat(filters): add No tags filter to transactions and shared pages

src/app/shared/page.tsx

@@ -40,12 +40,20 @@ function TagFilter({ value, onChange }: { value: string[]; onChange: (v: string[
     return () => document.removeEventListener("mousedown", handler);
   }, []);
 
-  if (!tags.length) return null;
-
-  const toggle = (id: string) =>
-    onChange(value.includes(id) ? value.filter((x) => x !== id) : [...value, id]);
+  const toggle = (id: string) => {
+    let next: string[];
+    if (value.includes(id)) {
+      next = value.filter((x) => x !== id);
+    } else if (id === "untagged") {
+      next = ["untagged"];
+    } else {
+      next = [...value.filter((x) => x !== "untagged"), id];
+    }
+    onChange(next);
+  };
 
   const label = value.length === 0 ? "All Tags"
+    : value.includes("untagged") ? "No tags"
     : value.length === 1 ? (tags.find((t) => String(t.id) === value[0])?.name ?? "1 tag")
     : `${value.length} tags`;
 
@@ -61,6 +69,11 @@ function TagFilter({ value, onChange }: { value: string[]; onChange: (v: string[
       </button>
       {open && (
         <div className="absolute top-full mt-1 z-20 bg-zinc-900 border border-zinc-700 rounded-lg shadow-xl min-w-[160px] max-h-56 overflow-y-auto">
+          <label className="flex items-center gap-2 px-3 py-1.5 hover:bg-zinc-800 cursor-pointer text-sm border-b border-zinc-800">
+            <input type="checkbox" checked={value.includes("untagged")} onChange={() => toggle("untagged")}
+              className="accent-indigo-500 flex-shrink-0" />
+            <span className="text-zinc-400 italic">No tags</span>
+          </label>
           {tags.map((t) => (
             <label key={t.id} className="flex items-center gap-2 px-3 py-1.5 hover:bg-zinc-800 cursor-pointer text-sm">
               <input type="checkbox" checked={value.includes(String(t.id))} onChange={() => toggle(String(t.id))}
@@ -259,8 +272,9 @@ function PaymentHistory({ participantId, currentUserId }: { participantId: numbe
 // ── Main page ─────────────────────────────────────────────────────────────────
 export default function SharedPage() {
   const [tagIds, setTagIds] = useState<string[]>([]);
+  const realTagIds = tagIds.filter((id) => id !== "untagged");
   const { data: transactions = [], isLoading: txLoading } = useSharedTransactions(tagIds);
-  const { data: balances = [], isLoading: balLoading } = useParticipantBalances(tagIds);
+  const { data: balances = [], isLoading: balLoading } = useParticipantBalances(realTagIds);
   const { data: me } = useCurrentUser();
   const [addingParticipant, setAddingParticipant] = useState(false);
   const [paymentModal, setPaymentModal] = useState<{ id: number; name: string; balance: number } | null>(null);