Adds `seed_notification_links`, which upserts one NotificationLink row per
action_code documented in docs/frontend-notification-click-actions.md (12
billboard + 15 escrow codes), each active with a sample url_template
(https://app.gooyal.ir/ads/{object_id} / .../escrow/{object_id}). Lets
producer notifications resolve a click_url end to end today; the real
routes still need confirming with whoever owns the frontend, and can be
edited any time via the Django admin. Run with --force to overwrite rows
that already exist; existing rows are otherwise left untouched so manual
admin edits aren't clobbered by a rerun.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
