test(integration): verify unread/starred cross views keep the acted-on row

Adds 11-cross-view-retain.spec.ts: with the Unread cross view open, reading a
mail keeps it in the list (status + unread counter update only, no removal);
with the Starred cross view open, un-starring keeps it. Both force the
focus/push refresh that previously dropped the row and assert it survives.

Supporting test hooks:
- thread-list-item: expose data-starred on the row.
- email-context-menu: testId ctx-star / ctx-unstar on the star item.
- integration helpers: expectEmailStarred (app.ts), setFlagged (jmap.ts).
- integration policy.json: enable crossStarredViewEnabled.

Verified: 08-shared-moves-style run of 11-cross-view-retain → 2/2 passed
against the dockerized stack.

components/email/email-context-menu.tsx

@@ -372,6 +372,7 @@ export function EmailContextMenu({
           label={isStarred ? t("unstar") : t("star")}
           onClick={() => handleAction(onToggleStar!)}
           disabled={!onToggleStar}
+          testId={isStarred ? "ctx-unstar" : "ctx-star"}
         />
       )}
 

components/email/thread-list-item.tsx

@@ -190,6 +190,7 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
         data-email-id={email.id}
         data-subject={email.subject || ''}
         data-unread={isUnread ? 'true' : 'false'}
+        data-starred={email.keywords?.$flagged ? 'true' : 'false'}
         className={cn(
           "relative group cursor-pointer select-none transition-shadow duration-200 border-b border-border overflow-hidden",
           resolvedRowTint ? resolvedRowTint : (