Add Expenses app

A UI based on [Budget Zen](https://github.com/BrunoBernardino/budgetzen-web) but slightly updated and adjusted for bewCloud. It also features a chart with available money and spent by budgets.

This is useful for envelope-based budgeting.

routes/expenses.tsx

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+import { Handlers, PageProps } from 'fresh/server.ts';
+
+import { Budget, Expense, FreshContextState, SupportedCurrencySymbol } from '/lib/types.ts';
+import { isAppEnabled } from '/lib/config.ts';
+import { generateMonthlyBudgetsAndExpenses, getBudgets, getExpenses } from '/lib/data/expenses.ts';
+import ExpensesWrapper from '/islands/expenses/ExpensesWrapper.tsx';
+
+interface Data {
+  userBudgets: Budget[];
+  userExpenses: Expense[];
+  initialMonth: string;
+  currency: SupportedCurrencySymbol;
+}
+
+export const handler: Handlers<Data, FreshContextState> = {
+  async GET(request, context) {
+    if (!context.state.user) {
+      return new Response('Redirect', { status: 303, headers: { 'Location': `/login` } });
+    }
+
+    if (!isAppEnabled('expenses')) {
+      return new Response('Redirect', { status: 303, headers: { 'Location': `/files` } });
+    }
+
+    const searchParams = new URL(request.url).searchParams;
+
+    let initialMonth = searchParams.get('month') || new Date().toISOString().substring(0, 7);
+
+    const currentMonth = new Date().toISOString().substring(0, 7);
+    const nextMonth = new Date(new Date(currentMonth).setUTCMonth(new Date(currentMonth).getUTCMonth() + 1))
+      .toISOString()
+      .substring(0, 7);
+
+    // Send invalid months (format) back to current month
+    if (!initialMonth.match(/^\d{4}-\d{2}$/)) {
+      initialMonth = currentMonth;
+    }
+
+    // Reset to next month if the selected month is too far in the future
+    if (initialMonth > nextMonth) {
+      initialMonth = nextMonth;
+    }
+
+    let userBudgets = await getBudgets(context.state.user.id, initialMonth);
+
+    let userExpenses = await getExpenses(context.state.user.id, initialMonth);
+
+    // If there are no budgets or expenses, and the selected month is in the future, generate the month's budgets and expenses
+    if (userBudgets.length === 0 && userExpenses.length === 0 && initialMonth >= currentMonth) {
+      await generateMonthlyBudgetsAndExpenses(context.state.user.id, initialMonth);
+
+      userBudgets = await getBudgets(context.state.user.id, initialMonth);
+      userExpenses = await getExpenses(context.state.user.id, initialMonth);
+    }
+
+    const currency = context.state.user.extra.expenses_currency || '$';
+
+    return await context.render({ userBudgets, userExpenses, initialMonth, currency });
+  },
+};
+
+export default function ExpensesPage({ data }: PageProps<Data, FreshContextState>) {
+  return (
+    <main>
+      <ExpensesWrapper
+        initialBudgets={data.userBudgets}
+        initialExpenses={data.userExpenses}
+        initialMonth={data.initialMonth}
+        currency={data.currency}
+      />
+    </main>
+  );
+}