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/connection_test.go

@@ -21,13 +21,6 @@ func TestUseRejectsNilSQL(t *testing.T) {
 	}
 }
 
-func TestCheckLocaleRejectsNilSQL(t *testing.T) {
-	err := CheckLocale(t.Context(), nil)
-	if err == nil || !strings.Contains(err.Error(), "sql db is nil") {
-		t.Fatalf("got %v", err)
-	}
-}
-
 func TestPublishRejectsNilHandles(t *testing.T) {
 	app := backpack.New(nil)
 	if err := Publish(nil, nil, nil); err == nil {
@@ -105,31 +98,6 @@ func TestSharedSQLPoolUsedByGORMAndClosed(t *testing.T) {
 	}
 }
 
-func TestWrongICULocaleFailsOpen(t *testing.T) {
-	admin := lagoonDB(t)
-	ctx := t.Context()
-	if _, err := admin.ExecContext(ctx, `CREATE DATABASE lagoon_locale_fail TEMPLATE template0 ENCODING 'UTF8' LOCALE_PROVIDER libc LOCALE 'C'`); err != nil && !strings.Contains(err.Error(), "already exists") {
-		t.Fatalf("create libc database: %v", err)
-	}
-	t.Cleanup(func() {
-		_, _ = admin.ExecContext(ctx, `DROP DATABASE IF EXISTS lagoon_locale_fail WITH (FORCE)`)
-	})
-	failDSN, err := dsnWithDB(lagoonDSN, "lagoon_locale_fail")
-	if err != nil {
-		t.Fatal(err)
-	}
-	_, _, err = Open(ctx, failDSN)
-	if err == nil {
-		t.Fatal("wrong locale must fail boot")
-	}
-	msg := err.Error()
-	for _, want := range []string{"ICU", "pl-PL", "CREATE DATABASE", "LOCALE_PROVIDER icu"} {
-		if !strings.Contains(msg, want) {
-			t.Fatalf("missing %q in %s", want, msg)
-		}
-	}
-}
-
 func TestOpenFromAppReadsDSN(t *testing.T) {
 	_, dsn := dedicatedDB(t, "lagoon_from_app")
 	dir := t.TempDir()