feat(shared): replace settle buttons with payment ledger

- New split_payments table records actual payments between participants
- Balance = total split obligations - total payments (splits never marked settled)
- Record Payment modal per participant: direction toggle, amount pre-filled with balance, date, notes
- Payment history inline on each balance card with +/- display and delete
- Per-transaction Settle button removed; Action column removed from shared table
- Splits always show the true cost breakdown regardless of payment state

src/lib/hooks.ts

@@ -257,11 +257,43 @@ export function useSetSplits() {
   });
 }
 
-export function useSettleSplits() {
+export interface SplitPayment {
+  id: number;
+  from_participant_id: number;
+  from_name: string;
+  to_participant_id: number;
+  to_name: string;
+  amount: number;
+  payment_date: string;
+  notes: string | null;
+  linked_transaction_id: number | null;
+  created_at: string;
+}
+
+export function usePaymentHistory(participantId: number | null) {
+  return useQuery<SplitPayment[]>({
+    queryKey: ["split-payments", participantId],
+    queryFn: async () => {
+      if (!participantId) return [];
+      const res = await fetch(`/api/split-payments?participant_id=${participantId}`);
+      return res.json();
+    },
+    enabled: !!participantId,
+  });
+}
+
+export function useRecordPayment() {
   const qc = useQueryClient();
   return useMutation({
-    mutationFn: async (body: { participant_id?: number; split_ids?: number[] }) => {
-      const res = await fetch("/api/splits/settle", {
+    mutationFn: async (body: {
+      from_participant_id: number;
+      to_participant_id: number;
+      amount: number;
+      payment_date: string;
+      notes?: string;
+      linked_transaction_id?: number;
+    }) => {
+      const res = await fetch("/api/split-payments", {
         method: "POST",
         headers: { "Content-Type": "application/json" },
         body: JSON.stringify(body),
@@ -269,8 +301,22 @@ export function useSettleSplits() {
       return res.json();
     },
     onSuccess: () => {
-      qc.invalidateQueries({ queryKey: ["shared-transactions"] });
       qc.invalidateQueries({ queryKey: ["participant-balances"] });
+      qc.invalidateQueries({ queryKey: ["split-payments"] });
+    },
+  });
+}
+
+export function useDeletePayment() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: async (id: number) => {
+      const res = await fetch(`/api/split-payments?id=${id}`, { method: "DELETE" });
+      return res.json();
+    },
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ["participant-balances"] });
+      qc.invalidateQueries({ queryKey: ["split-payments"] });
     },
   });
 }

src/lib/queries.ts

@@ -276,16 +276,17 @@ export interface ParticipantBalance {
 export async function getParticipantBalances(ownerId: number) {
   return queryRaw<ParticipantBalance>(`
     SELECT p.id, p.name,
-      COALESCE(SUM(combined.signed_amount), 0)::numeric(12,2) as total_owed,
-      COALESCE(SUM(combined.unsettled_count), 0)::int as unsettled_count
+      COALESCE(SUM(splits.signed_amount), 0)::numeric(12,2)
+        - COALESCE(payments.net_paid, 0)::numeric(12,2) AS total_owed,
+      COALESCE(SUM(splits.split_count), 0)::int AS unsettled_count
     FROM participants p
+
+    -- All split obligations (settled flag ignored — payments are the source of truth)
     LEFT JOIN (
       -- They owe me: their splits on transactions I own
       SELECT ts.participant_id AS pid,
-        CASE WHEN ts.settled = false
-          THEN (CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') THEN t.amount ELSE -t.amount END) * ts.share_percent / 100
-          ELSE 0 END AS signed_amount,
-        CASE WHEN ts.settled = false AND t.transaction_type IN ('debit', 'fee', 'interest') THEN 1 ELSE 0 END AS unsettled_count
+        (CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') THEN t.amount ELSE -t.amount END) * ts.share_percent / 100 AS signed_amount,
+        1 AS split_count
       FROM transaction_splits ts
       JOIN transactions t ON t.id = ts.transaction_id
       LEFT JOIN statements s ON s.id = t.statement_id
@@ -295,17 +296,26 @@ export async function getParticipantBalances(ownerId: number) {
 
       -- I owe them: my splits on transactions they own
       SELECT COALESCE(t.owner_id, s.owner_id) AS pid,
-        CASE WHEN ts.settled = false
-          THEN -(CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') THEN t.amount ELSE -t.amount END) * ts.share_percent / 100
-          ELSE 0 END AS signed_amount,
-        0 AS unsettled_count
+        -((CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') THEN t.amount ELSE -t.amount END) * ts.share_percent / 100) AS signed_amount,
+        0 AS split_count
       FROM transaction_splits ts
       JOIN transactions t ON t.id = ts.transaction_id
       LEFT JOIN statements s ON s.id = t.statement_id
       WHERE ts.participant_id = $1 AND COALESCE(t.owner_id, s.owner_id) != $1
-    ) combined ON combined.pid = p.id
+    ) splits ON splits.pid = p.id
+
+    -- Net payments: positive = they paid me, negative = I paid them
+    LEFT JOIN (
+      SELECT
+        CASE WHEN sp.from_participant_id != $1 THEN sp.from_participant_id ELSE sp.to_participant_id END AS pid,
+        SUM(CASE WHEN sp.to_participant_id = $1 THEN sp.amount ELSE -sp.amount END) AS net_paid
+      FROM split_payments sp
+      WHERE sp.from_participant_id = $1 OR sp.to_participant_id = $1
+      GROUP BY pid
+    ) payments ON payments.pid = p.id
+
     WHERE p.id != $1
-    GROUP BY p.id, p.name
+    GROUP BY p.id, p.name, payments.net_paid
     ORDER BY p.name
   `, [ownerId]);
 }