Notification

We need to create notification (SMS and Email) for buy request when off-takers is look for some product - farmers producing such produce should be notified
Same as sell notification - off-takers buying produce posted by farmer should be notified when farmer post

The issue names no files or tests; first locate the existing sell-notification implementation and trace how product posts are matched to recipients. Define the SMS and email behavior for both directions, then verify that farmers are notified for matching buy requests and off-takers for matching farmer posts.

Written by the indexing model from the issue text.