v1.3.0: cross-account transfer + Gmail offset fix

Added

• email_transfer tool — move or copy emails between accounts (e.g. iCloud/Outlook into Gmail) while preserving the original message intact (sender, date, threading) by transferring the raw MIME. With deleteAfter=true the source copy is trashed only after a confirmed import, making it a safe cross-account move. Backed by new optional provider primitives getRawMessage() / appendRawMessage() implemented for Gmail, IMAP+iCloud, and Outlook.

Fixed

• Gmail search offset was ignored, so paginating an inbox returned the same first page every time. Gmail's API has no numeric offset (only an opaque pageToken), so search() now pages forward through the lightweight message-id list to the offset + limit window and fetches full bodies only for that window. IMAP and Outlook already honored offset.