Add storage/postgresql redirect card

Links to services/postgresql for discoverability from storage section.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/reference/index.md

@@ -53,4 +53,5 @@ Cluster configuration and application registry.
 Network storage and backup configuration.
 
 - [[storage/sifaka|Sifaka]] - Synology NAS configuration
+- [[storage/postgresql|PostgreSQL]] - Database cluster
 - [[storage/backups|Backups]] - Backup policy and schedule

docs/reference/storage/postgresql.md

@@ -0,0 +1,10 @@
+---
+title: PostgreSQL
+tags:
+  - storage
+  - database
+---
+
+# PostgreSQL
+
+See [[services/postgresql|PostgreSQL]] in Services.