refactor: extract shared expense/report module into src/common

Collapse the Expenses page into a single src/Expense.tsx file and rename
the Reports page to src/Reports/Report.tsx, extracting their shared
transaction-list UI, date/grouping helpers, field configs, and types
into an expense/report-agnostic src/common module. Update ReportViewer
and GenerateReportPanel to consume the shared components, rewire
main.jsx imports, and remove the old src/Expense/ folder and
src/Reports/Reports.tsx.

src/common/types.ts

@@ -0,0 +1,29 @@
+import type { FieldConfig } from "../../react-openapi";
+
+export interface ExpenseItem {
+  id: string;
+  entity?: { name?: string; type?: string; logo?: string } | null;
+  amount: number;
+  account?: { name?: string; number?: string; type?: string; currency?: string } | null;
+  tags?: { icon?: string; name?: string }[];
+  occurred_at?: string;
+  created_at?: string;
+  updated_at?: string;
+}
+
+export interface GroupedMonth {
+  key: string;
+  items: ExpenseItem[];
+  spent: number;
+  income: number;
+  currency: string;
+}
+
+export interface TxnFieldConfigs {
+  entity: FieldConfig;
+  amount: FieldConfig;
+  account: FieldConfig;
+  occurredAt: FieldConfig;
+  logo: FieldConfig;
+  formats: { entity: string; account: string };
+}