feat(filters): smart query bar with amount operators and multi-select dropdowns

- Query bar parses >500, >=500, <500, <=500, 500-1500 into amount_min/max filters
- Parsed tokens shown as dismissable chips below the query bar
- Category, Bank, Tag, Type filters upgraded from single-select to multi-select
- MultiSelect dropdown component with checkbox list and active-state border
- Backend: TransactionFilters uses string[] for categories/bank_names/tag_ids/transaction_types
- SQL: ANY($n::text[]) / ANY($n::int[]) for array filters

src/app/insights/page.tsx

@@ -74,7 +74,7 @@ function DrillDownRow({
   from: string;
   to: string;
 }) {
-  const { data, isLoading } = useTransactions({ category, from, to, limit: 200 });
+  const { data, isLoading } = useTransactions({ categories: category ? [category] : [], from, to, limit: 200 });
   const updateTx = useUpdateTransaction();
 
   if (isLoading) {