fix(e2e): match an email template tab on its whole name, not a prefix

CI failed on a test nobody had touched:

    strict mode violation: getByRole('tab', { name: /Email address changed/ })
    resolved to 2 elements

The locators in AdminEmails built an unanchored regex from the label, so a template whose name merely began with another's matched both. #337 added "Email address changed by the shop" alongside "Email address changed" and broke the assertion above it.

The failure named the assertion rather than the new template, which is what made it worth more than a rename. It is the same shape as the switch locator that silently retargeted in #317: a loose locator that keeps passing until something new is added nearby, and then fails somewhere that says nothing about the cause.

So the fix is the locator rather than the label. One helper now builds a matcher anchored at both ends, allowing only the optional "Customised" suffix a tab carries once its template has been edited, and escaping the label because these are copy and copy acquires brackets and full stops eventually. Both railTab and customisedTab go through it, and callers pass plain strings instead of assembling regexes at each call site.

The new template is added to the list the test walks, which is what it should have had in #337.

Verified the matcher against every real label plus the pairs that collide, including that a customised-only match still rejects an unedited tab. Frontend tsc and lint clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/tests/e2e/email-templates.spec.ts

@@ -25,14 +25,18 @@ test.describe('Editing the customer emails', () => {
       'Favorited item sold',
       'Favorited item withdrawn',
       'Cart reminder',
-      'Email address changed'
+      'Email address changed',
+      // Added in #337, and the reason these are matched on the whole
+      // accessible name rather than as substrings: it extends the label above
+      // it, so an unanchored match resolved to both tabs.
+      'Email address changed by the shop'
     ]) {
-      await expect(adminEmails.railTab(new RegExp(label))).toBeVisible();
+      await expect(adminEmails.railTab(label)).toBeVisible();
     }
 
     // Only a customised template is marked, so which ones have been changed is
     // visible without opening each one. An untouched template carries nothing.
-    await expect(adminEmails.railTab(/Password reset/)).toBeVisible();
+    await expect(adminEmails.railTab('Password reset')).toBeVisible();
     await expect(adminEmails.customisedTab('Password reset')).toHaveCount(0);
   });