Fix bulk code vendor pre-population for single vs multi-client contexts

- vendor-default-account now uses raw vendor default account (not client-specific override)
- Account name is clientized via d-accounts/clientize only for single-client contexts
- Added single-client-id helper that returns client ID only when user has exactly one client
- Added multi-client e2e test verifying no pre-population across multiple clients
- Updated test server to support multi-client mode switching via /test-set-client-mode
- Test server now seeds a second client for multi-client scenarios

src/clj/auto_ap/ssr/transaction/bulk_code.clj

@@ -2,6 +2,7 @@
   (:require
    [auto-ap.datomic
     :refer [audit-transact-batch conn pull-attr pull-many]]
+   [auto-ap.datomic.accounts :as d-accounts]
    [auto-ap.logging :as alog]
    [auto-ap.permissions :refer [wrap-must]]
    [auto-ap.query-params :refer [wrap-copy-qp-pqp]]
@@ -324,14 +325,16 @@
                             [:p (str "Successfully coded " (count all-ids) " transactions.")])
          :headers {"hx-trigger" "refreshTable"})))))
 
-(defn- get-client-id [request]
-  (-> request :clients first :db/id))
-
 (defn- vendor-default-account [vendor-id client-id]
+  "Returns the vendor's standard default account. For single-client contexts,
+   the account name is clientized (tailored to the customer). For multi-client
+   contexts, the raw account name is used."
   (when vendor-id
     (let [vendor (edit/get-vendor vendor-id)
-          clientized (edit/clientize-vendor vendor client-id)]
-      (:vendor/default-account clientized))))
+          account (:vendor/default-account vendor)]
+      (if client-id
+        (d-accounts/clientize account client-id)
+        account))))
 
 (defn- build-default-account-row [account]
   {:db/id (str (java.util.UUID/randomUUID))
@@ -360,11 +363,17 @@
                                                                :index (count (fc/field-value))}
                                                               "New account")))))])))
 
+(defn- single-client-id [request]
+  "Returns the client ID if the user has access to exactly one client, nil otherwise."
+  (when (= 1 (count (:clients request)))
+    (-> request :clients first :db/id)))
+
 (defn vendor-changed-handler [request]
   (let [snapshot (:snapshot (:multi-form-state request))
         step-params (:step-params (:multi-form-state request))
-        client-id (get-client-id request)
+        client-id (single-client-id request)
         vendor-id (or (:vendor step-params) (:vendor snapshot))
+        _ (println ::VENDOR-CHANGED :client-id client-id :vendor-id vendor-id :accounts-empty (empty? (:accounts step-params)))
         updated-step-params (if (and (empty? (:accounts step-params))
                                      vendor-id
                                      client-id)