test(e2e): convert the favorites, availability and orders specs (#137)

favorites, favorites-filter, sold-filter, orders and pending-publish. Five more copies of "register a customer" and three more of the hardcoded base URL go with them.

Two locators that were hiding real knowledge are now named. `gridCell` is the item's whole antd column rather than its card, needed because the SOLD ribbon renders outside the card — three specs reached for `.ant-col` directly to get at it. And `chooseAvailability` goes through the title attribute because antd's Segmented hides the real radio behind a styled label, so the input is found by role and cannot be clicked; that fact was written out twice in comments and is now written once in code.

The favorite control is located page-wide rather than within a card. The storefront paginates as items accumulate and the control is named for its item anyway, so scoping to a card bought nothing and broke whenever the card was on another page.

favorites-filter keeps its local `favorite()` helper. It is genuinely local — decline the opt-in, wait for the fading modal to stop intercepting pointer events, confirm the heart flipped — and belongs to that file's subject rather than to the storefront. It now takes page objects as parameters instead of reaching for locators itself, which is what a spec-level helper should look like.

Two specs still drive the registration form rather than taking the `customer` fixture, and deliberately. Both are about a signed-out visitor being interrupted mid-action — favoriting an item, or switching on the favorites filter — and the claim is that the thing they asked for survives the interruption. Replacing the interruption with an API call would delete the test.

Verified: favorites 6/6, favorites-filter 7/7, sold-filter 6/6, orders and pending-publish 8/8. Notably favorites-filter's "keeps showing a favorite after it sells" passes, which had been failing on a strict-mode violation from two items sharing a name across runs.

Refs #137

frontend/tests/e2e/pages/AccountModal.ts

@@ -17,6 +17,8 @@ export class AccountModal {
   readonly closeButton: Locator;
   readonly resendVerificationButton: Locator;
   readonly themeSwitches: Locator;
+  /** The second switch in the modal; the first is the theme. */
+  readonly favoriteAlertsSwitch: Locator;
   readonly notVerifiedNotice: Locator;
 
   readonly firstName: Locator;
@@ -44,6 +46,7 @@ export class AccountModal {
     this.closeButton = this.dialog.getByRole('button', { name: 'Close' });
     this.resendVerificationButton = this.dialog.getByRole('button', { name: 'Send it again' });
     this.themeSwitches = this.dialog.getByRole('switch');
+    this.favoriteAlertsSwitch = this.dialog.getByRole('switch').last();
     this.notVerifiedNotice = this.dialog.getByText('Email not verified');
 
     this.firstName = this.dialog.getByLabel('First name', { exact: true });