fix: Add defer.close for all queries

.entire/metadata/42401d2e-7d1c-4c0e-abe6-356cb2d48747/summary.txt

@@ -0,0 +1,7 @@
+All changes are already in place and verified:
+
+- **Build**: passes
+- **go vet**: passes  
+- **Tests**: pass
+
+The changes are currently unstaged. All 16 locations from the plan have been fixed — `defer rows.Close()` added after each `Query()` error check, manual `rows.Close()` calls in error paths removed, and `rows.Err()` checks added where missing. The `AddJobCount` function was also simplified from `Query` + loop to `QueryRow().Scan()` since it returns a single value.