feat: disciple link

migrations/0046_create_disciple_announcements.up.sql

@@ -0,0 +1,20 @@
+-- One row per account whose arrival as a direct disciple of Śrīla Prabhupāda
+-- has been announced to the community.
+--
+-- This table exists purely for idempotency. Announcing writes a notification
+-- to *every* user, so it must happen at most once per devotee — not again when
+-- an admin corrects which disciple record they're linked to, not again on a
+-- double-clicked button, and not again if the process restarts mid-fan-out.
+-- The insert is `ON CONFLICT DO NOTHING` and only a caller that actually
+-- inserted the row goes on to broadcast, which makes the guard atomic.
+--
+-- Keyed on user_id (not disciple_id) deliberately: we are announcing that a
+-- *person* has joined. Re-pointing their link at a different disciple record
+-- corrects a mistake; it isn't a second arrival.
+CREATE TABLE IF NOT EXISTS disciple_announcements (
+    user_id      UUID        PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+    -- The Mongo disciple ObjectID they were linked to at announcement time,
+    -- kept for auditing (which record prompted the announcement).
+    disciple_id  TEXT        NOT NULL,
+    announced_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);