feat(finance): Phase 6 — Budget & Analytics

Add monthly budgets per category with spend-vs-budget dashboard and 6-month trend table.
Includes upsert budget API, monthly analytics endpoint, inline budget editing, and route auth fixes.

src/lib/hooks.ts

@@ -352,3 +352,72 @@ export function useCreateParticipant() {
     },
   });
 }
+
+// --- Budgets & Analytics ---
+
+export interface BudgetRow {
+  id: number;
+  category: string;
+  month: string;
+  amount_limit: number;
+}
+
+export interface MonthlyAnalyticsRow {
+  category: string;
+  spent: Record<string, number>;
+  budget: Record<string, number>;
+  txCount: Record<string, number>;
+}
+
+export interface MonthlyAnalytics {
+  months: string[];
+  rows: MonthlyAnalyticsRow[];
+  totals: Record<string, { spent: number; budget: number }>;
+}
+
+export function useBudgets(month: string) {
+  return useQuery<BudgetRow[]>({
+    queryKey: ["budgets", month],
+    queryFn: async () => {
+      const res = await fetch(`/api/budgets?month=${month}`);
+      return res.json();
+    },
+  });
+}
+
+export function useUpsertBudget() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: async (data: { category: string; month: string; amount_limit: number }) => {
+      const res = await fetch("/api/budgets", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify(data),
+      });
+      if (!res.ok) throw new Error("Failed to save budget");
+      return res.json();
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["budgets"] }),
+  });
+}
+
+export function useDeleteBudget() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: async (id: number) => {
+      await fetch(`/api/budgets/${id}`, { method: "DELETE" });
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["budgets"] }),
+  });
+}
+
+export function useMonthlyAnalytics(months?: number) {
+  const m = months || 6;
+  return useQuery<MonthlyAnalytics>({
+    queryKey: ["analytics", "monthly", m],
+    queryFn: async () => {
+      const res = await fetch(`/api/analytics/monthly?months=${m}`);
+      return res.json();
+    },
+  });
+}