Sync Plaid transactions using the cursor-based /transactions/sync endpoint and handle all update types

Steps

1. On first sync, call POST /transactions/sync with access_token and no cursor; store the next_cursor from the response and process all items in the added array
2. On subsequent syncs, pass the stored cursor in the request body; the response returns added, modified, and removed arrays representing changes since the last cursor position
3. Upsert records from added and modified into your transaction store using transaction_id as the stable key; delete or tombstone records whose transaction_ids appear in removed
4. If has_more is true in the response, immediately call /transactions/sync again with the new next_cursor until has_more is false — do not wait for a webhook between pages
5. Subscribe to the TRANSACTIONS webhook (transactions sync_updates_available) and trigger a sync cycle when you receive it rather than polling on a fixed schedule
6. Handle TRANSACTIONS_REMOVED webhooks separately if your integration listens for them; reconcile any removed transaction_ids against your store even if you did not initiate a sync