feat(lagoon): per-query collation for OrderBy, drop the database locale check

- lagoon.OrderBy takes variadic lagoon.OrderOption values; lagoon.Collate(name)
  emits a validated, double-quoted COLLATE clause (e.g. "pl-x-icu")
- remove the exported CheckLocale and the ICU pl-PL check from Open and Use
- framework test containers and per-test databases are plain PostgreSQL
- lagoon README, root README and docs pages drop the locale requirement;
  queries-and-pagination gains a "Sorting with a collation" section
  backed by ExampleCollate

modules/lagoon/export_docs_test.go

@@ -6,8 +6,8 @@ import (
 	"gorm.io/gorm"
 )
 
-// DocsDB returns a GORM handle on a fresh ICU pl-PL database named name in
-// this package's Postgres harness, for the database-backed docs examples in
+// DocsDB returns a GORM handle on a fresh database named name in this
+// package's Postgres harness, for the database-backed docs examples in
 // example_test.go. It skips under -short and fails when the harness has no
 // database, like the package's other database tests.
 func DocsDB(t *testing.T, name string) *gorm.DB {