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

docs/examples/blog/postgres_test.go

@@ -100,10 +100,9 @@ func stopPostgres() {
 	}
 }
 
-// icuDatabase creates a database for one test with the ICU pl-PL locale
-// lagoon requires, and drops it when the test ends. It returns the pool
-// opened on it and its DSN.
-func icuDatabase(t *testing.T) (*sql.DB, string) {
+// testDatabase creates a database for one test and drops it when the test
+// ends. It returns the pool opened on it and its DSN.
+func testDatabase(t *testing.T) (*sql.DB, string) {
 	t.Helper()
 	if testing.Short() {
 		t.Skip("requires testcontainers postgres")
@@ -113,7 +112,7 @@ func icuDatabase(t *testing.T) (*sql.DB, string) {
 	}
 	name := "blog_" + strings.ToLower(strings.NewReplacer("/", "_", "-", "_").Replace(t.Name()))
 	quoted := `"` + strings.ReplaceAll(name, `"`, `""`) + `"`
-	if _, err := pgAdmin.ExecContext(t.Context(), `CREATE DATABASE `+quoted+` TEMPLATE template0 ENCODING 'UTF8' LOCALE_PROVIDER icu ICU_LOCALE 'pl-PL'`); err != nil {
+	if _, err := pgAdmin.ExecContext(t.Context(), `CREATE DATABASE `+quoted+` TEMPLATE template0 ENCODING 'UTF8'`); err != nil {
 		t.Fatalf("create %s: %v", name, err)
 	}
 	u, err := url.Parse(pgDSN)
@@ -133,11 +132,11 @@ func icuDatabase(t *testing.T) (*sql.DB, string) {
 	return db, dsn
 }
 
-// migrated activates acme.blog, migrates a fresh ICU database and publishes
+// migrated activates acme.blog, migrates a fresh database and publishes
 // it on the application, as the serve command does at start-up.
 func migrated(t *testing.T) (*backpack.App, party.Plugin, *gorm.DB) {
 	t.Helper()
-	sqlDB, _ := icuDatabase(t)
+	sqlDB, _ := testDatabase(t)
 	gdb, err := lagoon.Use(t.Context(), sqlDB)
 	if err != nil {
 		t.Fatalf("lagoon.Use: %v", err)