Import Vendor Export Upload

Import a ChatGPT or Claude data export into the caller's own Mind.

Accepts the vendor's export zip (only its conversations.json member is ever read) or a bare conversations.json. Every conversation is ingested through the same path a live capture uses, so it lands in the caller's Mind the same way. Makes zero AI-provider calls.

Small exports (conversations.json at or under SYNC_IMPORT_JSON_MEMBER_BYTES) are imported inline and the response already carries the final counts. Larger ones run as a background task; poll GET /import-export/{id} for the result.

The body is read in _UPLOAD_READ_CHUNK_BYTES chunks rather than in one file.read() call, so an over-the-cap upload is rejected as soon as the running total crosses MAX_EXPORT_UPLOAD_BYTES instead of after buffering the whole thing. A present Content-Length already over the cap is rejected before any read at all.