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/utils/fieldConfigs.ts

@@ -0,0 +1,26 @@
+import type { ResourceConfig } from "../../../react-openapi";
+import type { TxnFieldConfigs } from "../types";
+
+export function buildTxnFieldConfigs(resources: ResourceConfig[]): TxnFieldConfigs | null {
+  const expensesRes = resources.find((r) => r.name === "expenses");
+  const entitiesRes = resources.find((r) => r.name === "entities");
+  const accountsRes = resources.find((r) => r.name === "accounts");
+  const find = (res: ResourceConfig | undefined, name: string) => res?.fields.find((f) => f.name === name);
+  const entity = find(expensesRes, "entity");
+  const amount = find(expensesRes, "amount");
+  const account = find(expensesRes, "account");
+  const occurredAt = find(expensesRes, "occurred_at");
+  const logo = find(entitiesRes, "logo");
+  if (!entity || !amount || !account || !occurredAt || !logo) return null;
+  return {
+    entity,
+    amount,
+    account,
+    occurredAt,
+    logo,
+    formats: {
+      entity: entitiesRes?.displayFormat ?? "{name}",
+      account: accountsRes?.displayFormat ?? "{name}",
+    },
+  };
+}