Fix add-form JS: name→sort-name sync and related-game disable

Two bugs in the add forms, both root-caused via the e2e harness:

1. add_game Name → Sort name never synced. syncSelectInputUntilChanged was
   scoped to "form", but the first <form> on every page is the navbar logout
   form — the add-form fields live in a later form, so the delegated listener
   never heard their events. Scope to "#add-form" (the add-form wrapper). Also
   switch the sync from the "change" event to "input" so Sort name mirrors Name
   live as you type, not only on blur.

2. add_purchase Related game not disabled when Type == Game.
   disableElementsWhenTrue set `.disabled` on #id_related_game, which is the
   SearchSelect wrapper <div> (a <div> ignores `disabled`). Target the inner
   [data-search-select-search] input instead, so the widget is actually disabled.

Adds two e2e regression tests (live sync; type-game disables the related-game
search input and re-enables it for other types).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

e2e/test_widgets_e2e.py

@@ -147,3 +147,28 @@ def test_add_purchase_related_game_is_flat_game_search(
     related = page.locator('[data-search-select][data-name="related_game"]')
     expect(related).to_have_count(1)
     expect(related).to_have_attribute("data-search-url", "/api/games/search")
+
+
+def test_add_game_syncs_sort_name_from_name(authenticated_page: Page, live_server):
+    """Typing into Name live-fills Sort name (sync bound to the add form, not
+    the navbar logout form which is the first <form> on the page)."""
+    page = authenticated_page
+    page.goto(f"{live_server.url}{reverse('games:add_game')}")
+    page.locator("#id_name").click()
+    page.locator("#id_name").type("Halo")
+    expect(page.locator("#id_sort_name")).to_have_value("Halo")
+
+
+def test_add_purchase_type_game_disables_related_game_search(
+    authenticated_page: Page, live_server
+):
+    """When Type is 'game', the related-game SearchSelect is disabled — the
+    real disable target is the inner search input, not the wrapper <div>
+    (a <div> ignores the disabled property)."""
+    page = authenticated_page
+    page.goto(f"{live_server.url}{reverse('games:add_purchase')}")
+    search = page.locator('#id_related_game [data-search-select-search]')
+    page.select_option("#id_type", "game")
+    expect(search).to_be_disabled()
+    page.select_option("#id_type", "dlc")
+    expect(search).to_be_enabled()

ts/add_game.ts

@@ -9,4 +9,6 @@ const syncData = [
   },
 ];
 
-syncSelectInputUntilChanged(syncData, "form");
+// Scope to the add form (#add-form), not "form": the first <form> on the page
+// is the navbar logout form, which never contains these fields.
+syncSelectInputUntilChanged(syncData, "#add-form");

ts/add_purchase.ts

@@ -53,7 +53,12 @@ onSwap("#id_separate_prices", (checkbox) => {
 });
 
 function setupElementHandlers(): void {
-  disableElementsWhenTrue("#id_type", "game", ["#id_name", "#id_related_game"]);
+  // related_game is a SearchSelect: its #id_related_game wrapper is a <div>
+  // (ignores `disabled`), so target the inner search <input> instead.
+  disableElementsWhenTrue("#id_type", "game", [
+    "#id_name",
+    "#id_related_game [data-search-select-search]",
+  ]);
 }
 
 onSwap("#id_type", (typeSelect) => {

ts/utils.ts

@@ -52,11 +52,12 @@ function syncSelectInputUntilChanged(syncData: Array<{ source: string; target: s
     console.error(`The parent selector "${parentSelector}" is not valid.`);
     return;
   }
-  // Set up a single change event listener on the document for handling all source changes
+  // One delegated "input" listener handles every source. "input" (not "change")
-  parentElement.addEventListener("change", function (event) {
+  // makes the mirror live as the user types, instead of only on blur.
+  parentElement.addEventListener("input", function (event) {
     // Loop through each sync configuration item
     syncData.forEach((syncItem: { source: string; target: string; source_value: string; target_value: string }) => {
-      // Check if the change event target matches the source selector
+      // Check if the event target matches the source selector
       if ((event.target as HTMLElement).matches(syncItem.source)) {
         if (!event.target) return;
         const sourceElement = event.target;