feat(analytics): cashflow view with income/investment/net — split-adjusted + multi-currency

- Add 'investment' category (shares, ETFs, super)
- Analytics API: separate income, investment, expense queries; use amount_aud for FX-aware sums
- Analytics page: cashflow summary (income/expenses/invested/net cash), grouped bar chart,
  income + invested rows in 6-month trend table
- MonthlyAnalytics interface: add income, investments, net fields to totals
- DB: amount_aud + exchange_rate_to_aud columns added and backfilled (in prior migration)

src/lib/categories.ts

@@ -16,6 +16,7 @@ export const CATEGORIES = [
   "rent",
   "transfers",
   "income",
+  "investment",
   "personal_care",
   "pets",
   "gifts",

src/lib/hooks.ts

@@ -451,7 +451,9 @@ export interface MonthlyAnalyticsRow {
 export interface MonthlyAnalytics {
   months: string[];
   rows: MonthlyAnalyticsRow[];
-  totals: Record<string, { spent: number; budget: number }>;
+  income: Record<string, number>;
+  investments: Record<string, number>;
+  totals: Record<string, { spent: number; income: number; investments: number; net: number }>;
 }
 
 export function useBudgets(month: string) {