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/migrations_test.go

@@ -39,22 +39,6 @@ func TestHistoryTableName(t *testing.T) {
 	}
 }
 
-func TestCheckLocaleMessage(t *testing.T) {
-	if err := checkLocale("i", "pl-PL"); err != nil {
-		t.Fatal(err)
-	}
-	err := checkLocale("c", "en_US")
-	if err == nil {
-		t.Fatal("want locale error")
-	}
-	msg := err.Error()
-	for _, want := range []string{"ICU", "pl-PL", "CREATE DATABASE", "LOCALE_PROVIDER icu", "en_US"} {
-		if !strings.Contains(msg, want) {
-			t.Fatalf("missing %q in %s", want, msg)
-		}
-	}
-}
-
 func TestRuntimeCommandsRegisterBareAndColonNames(t *testing.T) {
 	cmds := RuntimeCommands(nil, nil)
 	names := map[string]bool{}