fix: route all counter updates to the email's own account in aggregate views

Extend the counter-routing fix beyond markAsRead to every optimistic mailbox
counter update, so a different account's email never adjusts the active
account's folder counters (JMAP ids can collide across accounts).

- Add applyBatchMailboxCounterUpdate() + applyDeleteCounters() and apply the
  per-account routing to: deleteEmail (trash + permanent), moveToMailbox,
  moveEmailsToMailbox, batchMarkAsRead, batchDelete, and markThreadAsRead.
- markAsSpam/batchMarkAsSpam/batchMoveToMailbox don't touch counters (rely on
  refresh) and folder-level ops (rename/empty/markMailboxAsRead) are already
  account-scoped — left as-is.
- Test: batchMarkAsRead adjusts each account's counter in its own list.

stores/__tests__/email-store-unified-actions.test.ts

@@ -53,6 +53,7 @@ function makeClient() {
     markAsRead: vi.fn().mockResolvedValue(undefined),
     toggleStar: vi.fn().mockResolvedValue(undefined),
     moveEmail: vi.fn().mockResolvedValue(undefined),
+    batchMarkAsRead: vi.fn().mockResolvedValue(undefined),
   } as unknown as IJMAPClient;
 }
 
@@ -146,6 +147,27 @@ describe('unified-view single-email action routing (#281)', () => {
     expect(s.accountMailboxes['account-a'][0].unreadEmails).toBe(5); // active list untouched
   });
 
+  it('batchMarkAsRead adjusts each email’s own account counter (cross-account)', async () => {
+    useEmailStore.setState({
+      mailboxes: [makeMailbox({ id: 'inbox', role: 'inbox', unreadEmails: 5 })],
+      accountMailboxes: {
+        'account-a': [makeMailbox({ id: 'inbox', role: 'inbox', unreadEmails: 5 })],
+        'account-b': [makeMailbox({ id: 'inbox', role: 'inbox', unreadEmails: 3 })],
+      },
+      emails: [
+        makeEmail({ id: 'a1', sourceClientAccountId: 'account-a', sourceAccountId: 'account-a', keywords: {}, mailboxIds: { inbox: true } }),
+        makeEmail({ id: 'b1', sourceClientAccountId: 'account-b', sourceAccountId: 'account-b', keywords: {}, mailboxIds: { inbox: true } }),
+      ],
+      selectedEmailIds: new Set(['a1', 'b1']),
+    });
+
+    await useEmailStore.getState().batchMarkAsRead(activeClient, true);
+
+    const s = useEmailStore.getState();
+    expect(s.mailboxes[0].unreadEmails).toBe(4);                     // active account: -1
+    expect(s.accountMailboxes['account-b'][0].unreadEmails).toBe(2); // account-b: -1
+  });
+
   it('routes a shared/group email through the delegating login client + owner accountId', async () => {
     await useEmailStore.getState().markAsRead(activeClient, 'email-shared', true);
     // Reached via account-a's client (the active one), targeting the owner account.