In the unified All mail / Unread / Starred views, deleting (or moving /
marking read) a message from a shared/group folder left that folder's
sidebar counter at its old value.
Root cause: lib/unified-mailbox.ts decorates shared emails WITHOUT
namespacing their `mailboxIds`, so they carry the owner's bare JMAP ids,
while the shared mailbox is stored with a namespaced id (`${ownerId}:${origId}`)
and `isShared: true`. `emailInMailbox` only matched the namespaced `mailbox.id`
and disabled the `originalId` fallback for shared mailboxes, so no shared
email ever matched its folder and the counter math skipped it.
Match shared mailboxes via `originalId` too, scoped to the owning account
(`sourceAccountId === mailbox.accountId`) so a bare owner id can't collide
with another account's folder. This is the single matching helper used by all
counter paths (delete/move/markRead/spam), so they're all fixed at once.
Adds a regression test covering deletion of a shared-folder email in the
unified view.
Stefan Hildebrandt
fdad60cf03