Fix remaining PostgreSQL reference bugs

Make temporal, upgrade, and replication examples runnable without omitted dependencies or misleading worker rows.

skills/postgres-best-practices/references/logical-replication.md

@@ -382,7 +382,10 @@ SELECT
     now() - st.latest_end_time AS time_lag
 FROM pg_subscription s
 JOIN pg_stat_subscription st ON st.subid = s.oid
-WHERE st.pid IS NOT NULL;
+WHERE st.pid IS NOT NULL
+    AND st.relid IS NULL
+    -- PG17+ can also expose parallel apply workers; keep only the leader.
+    AND coalesce(to_jsonb(st)->>'worker_type', 'apply') = 'apply';
 ```
 
 ## Schema Changes During Replication

skills/postgres-best-practices/references/major-version-upgrades.md

@@ -226,8 +226,11 @@ Never upgrade production first. Test on a copy:
 # Create a test copy
 pg_basebackup -D /tmp/upgrade_test -Fp -Xs -P
 
+# Initialize an empty target cluster with the new version's binaries
+/usr/lib/postgresql/17/bin/initdb -D /tmp/new_cluster
+
 # Run pg_upgrade --check against the copy
-pg_upgrade --check \
+/usr/lib/postgresql/17/bin/pg_upgrade --check \
     --old-datadir /tmp/upgrade_test \
     --new-datadir /tmp/new_cluster \
     --old-bindir /usr/lib/postgresql/16/bin \

skills/postgres-best-practices/references/schema-design.md

@@ -173,6 +173,8 @@ This prevents overlapping bookings for the same room at the database level.
 PG18 adds built-in temporal constraint support, simplifying the exclusion constraint pattern above:
 
 ```sql
+CREATE EXTENSION IF NOT EXISTS btree_gist;
+
 CREATE TABLE room_bookings (
     room_id int NOT NULL,
     during tstzrange NOT NULL,