merged from gramsrv upstream

deploy/migrations/20260901000002_channel_stats_read_model.up.sql

@@ -0,0 +1,18 @@
+-- Bounded stats reads: event-time viewers, membership snapshots, and exact
+-- public-forward seek pagination by the durable MessageForward JSON shape.
+CREATE INDEX channel_message_viewers_stats_date_idx
+    ON public.channel_message_viewers (channel_id, viewed_at, viewer_user_id, message_id);
+
+CREATE INDEX channel_members_stats_period_idx
+    ON public.channel_members (channel_id, joined_at, left_at, user_id);
+
+CREATE INDEX channel_messages_public_forward_source_seek_idx
+    ON public.channel_messages (
+        (fwd_from #>> '{From,Type}'),
+        (fwd_from #>> '{From,ID}'),
+        (fwd_from #>> '{ChannelPost}'),
+        message_date DESC,
+        channel_id ASC,
+        id DESC
+    )
+    WHERE NOT deleted AND fwd_from <> '{}'::jsonb;