feat(expenses): add import functionality for expenses and total pending calculation

apps/frontend/src/lib/api.ts

@@ -188,6 +188,10 @@ export function getExpenses(status?: string, page?: number, pageSize?: number):
   return fetcher<PaginatedResponse<Expense>>(`/api/expenses${qs ? `?${qs}` : ""}`);
 }
 
+export function getTotalPending(): Promise<MonthlyExpensesTotal> {
+  return fetcher<MonthlyExpensesTotal>("/api/expenses/pending-total");
+}
+
 export function getMonthlyTotals(year?: number, month?: number): Promise<MonthlyTotals> {
   const params = new URLSearchParams();
   if (year) params.set("year", String(year));
@@ -202,3 +206,41 @@ export function createNonPeriodicExpense(data: CreateNonPeriodicExpenseInput): P
 export function payExpense(id: number, data: PayExpenseInput): Promise<Expense> {
   return mutator<Expense>(`/api/expenses/${id}/pay`, "PUT", data);
 }
+
+export type ImportResult = {
+  imported: number;
+  skipped: number;
+  skippedNoPeriods: number;
+  skippedDuplicate: number;
+  errors?: string[];
+};
+
+export type ImportExpensesResult = {
+  imported: number;
+  skipped: number;
+  errors?: string[];
+};
+
+export function importExpenses(file: File): Promise<ImportExpensesResult> {
+  const formData = new FormData();
+  formData.append("file", file);
+  return fetch("/api/expenses/import", {
+    method: "POST",
+    body: formData,
+  }).then((r) => {
+    if (!r.ok) throw new Error(`API error: ${r.status} ${r.statusText}`);
+    return r.json();
+  });
+}
+
+export function importPeriodicExpenses(file: File): Promise<ImportResult> {
+  const formData = new FormData();
+  formData.append("file", file);
+  return fetch("/api/periodic-expenses/import", {
+    method: "POST",
+    body: formData,
+  }).then((r) => {
+    if (!r.ok) throw new Error(`API error: ${r.status} ${r.statusText}`);
+    return r.json();
+  });
+}