Add error message to require-approval validator

Ensure the validation error message shows up properly when users try
to approve a manual transaction without assigning financial accounts.

src/clj/auto_ap/ssr/transaction/edit.clj

@@ -62,9 +62,10 @@
 
 (defn require-approval [s]
   [:and s
-   [:fn (fn [{:transaction/keys [accounts approval-status]}]
-          (or (not= approval-status :transaction-approval-status/approved)
-              (seq accounts)))]])
+   [:fn {:error/message "Approved transactions must have accounts assigned."}
+    (fn [{:transaction/keys [accounts approval-status]}]
+      (or (not= approval-status :transaction-approval-status/approved)
+           (seq accounts)))]])
 
 (def edit-form-schema
   (mc/schema