Upsert snoozes and mark snoozed messages as read

server/migrations/20250630023836_snooze.up.sql

@@ -1,6 +1,6 @@
 -- Add up migration script here
 CREATE TABLE IF NOT EXISTS snooze (
     id integer NOT NULL GENERATED ALWAYS AS IDENTITY,
-    message_id text NOT NULL,
+    message_id text NOT NULL UNIQUE,
     wake timestamptz NOT NULL
 );