graph/db+sqldb: impl PutClosedScid and IsClosedScid

sqldb/sqlc/queries/graph.sql

@@ -709,3 +709,20 @@ LIMIT 1;
 DELETE FROM prune_log
 WHERE block_height >= @start_height
   AND block_height <= @end_height;
+
+/* ─────────────────────────────────────────────
+   closed_scid table queries
+   ────────────────────────────────────────────-
+*/
+
+-- name: InsertClosedChannel :exec
+INSERT INTO closed_scids (scid)
+VALUES ($1)
+ON CONFLICT (scid) DO NOTHING;
+
+-- name: IsClosedChannel :one
+SELECT EXISTS (
+    SELECT 1
+    FROM closed_scids
+    WHERE scid = $1
+);