Delete Memory

Delete a memory by id, from every store it lives in.

Goes through the single deletion path (deletion.delete_memory): the active-tier copy, the engine node and the vectors that name it, the copies consolidation made of it, the deleted-memories ledger and its edit history. This route used to tombstone only the engine node, so the active copy kept answering recall and consolidation could write the text back. Tombstones are hidden from every read path; bytes are reclaimed by the sleep cycle, not here.