refactor(db): normalize asn prefix cache and ttl cleanup

Строки asn_prefix_cache_row; периодический prune через evobgp-ingest.

Co-authored-by: Cursor <cursoragent@cursor.com>

migrations/postgres/000020_asn_cache_rows.down.sql

@@ -0,0 +1,10 @@
+ALTER TABLE asn_prefix_cache ADD COLUMN prefixes_json JSONB NOT NULL DEFAULT '[]';
+
+UPDATE asn_prefix_cache apc
+SET prefixes_json = COALESCE((
+    SELECT jsonb_agg(apcr.prefix::text ORDER BY apcr.prefix::text)
+    FROM asn_prefix_cache_row apcr
+    WHERE apcr.asn = apc.asn
+), '[]'::jsonb);
+
+DROP TABLE IF EXISTS asn_prefix_cache_row;