Moving a message to a folder in another account (own ↔ delegated/shared) via the
"Move to" context menu was a no-op — the handlers always issued a single-account
Email/set, which can't move between JMAP accounts. Drag-and-drop already routed
these correctly; the context menu never did.
Add moveToMailboxCrossAware: it detects a cross-account destination (own and
shared mailboxes both carry accountId) and routes through the drag-and-drop
crossAccountMoveEmails pipeline, else falls back to the single-account move.
Fix the pipeline for delegated folders too: a client can't stage a blob in a
delegated account (Blob/upload → blobNotFound), so importing into a shared folder
failed. When one client reaches both accounts, use a server-side JMAP Email/copy
(+ destroy original) instead of blob copy+import; the blob path is kept only for
separate cross-server login accounts. Adds client.copyEmailAcrossAccounts.
Unit tests for the dispatch; the two 08-shared-moves specs are un-pinned. Full
docker integration suite green (37 passed).
Stefan Hildebrandt
15ad783848