feat(finance): Phase 5 — Rules Engine

Add rules engine with CRUD API, condition/action evaluation, and apply-all endpoint.
UI: rule builder form with field/operator/value conditions, tag multi-select, apply button with result stats.

src/lib/hooks.ts

@@ -352,3 +352,82 @@ export function useCreateParticipant() {
     },
   });
 }
+
+// --- Rules ---
+
+export interface RuleRow {
+  id: number;
+  name: string;
+  conditions: { field: string; operator: string; value: string }[];
+  actions: { set_category?: string; add_tag_ids?: number[]; set_merchant?: string };
+  enabled: boolean;
+  priority: number;
+  created_at: string;
+}
+
+export function useRules() {
+  return useQuery<RuleRow[]>({
+    queryKey: ["rules"],
+    queryFn: async () => {
+      const res = await fetch("/api/rules");
+      return res.json();
+    },
+  });
+}
+
+export function useCreateRule() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: async (data: Omit<RuleRow, "id" | "created_at">) => {
+      const res = await fetch("/api/rules", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify(data),
+      });
+      if (!res.ok) throw new Error("Failed to create rule");
+      return res.json();
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["rules"] }),
+  });
+}
+
+export function useUpdateRule() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: async ({ id, ...data }: Partial<RuleRow> & { id: number }) => {
+      const res = await fetch(`/api/rules/${id}`, {
+        method: "PATCH",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify(data),
+      });
+      if (!res.ok) throw new Error("Failed to update rule");
+      return res.json();
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["rules"] }),
+  });
+}
+
+export function useDeleteRule() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: async (id: number) => {
+      await fetch(`/api/rules/${id}`, { method: "DELETE" });
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["rules"] }),
+  });
+}
+
+export function useApplyRules() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: async () => {
+      const res = await fetch("/api/rules/apply", { method: "POST" });
+      if (!res.ok) throw new Error("Failed to apply rules");
+      return res.json() as Promise<{ matched: number; transactions_affected: number }>;
+    },
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ["transactions"] });
+      qc.invalidateQueries({ queryKey: ["rules"] });
+    },
+  });
+}