fix: harden module lifecycle and debug log setup

Export CurrentDialect(), return setup errors when debug logger is not
registered, and guard DestName logging when the module is uninitialized.

Co-authored-by: Cursor <cursoragent@cursor.com>

module_test.go

@@ -0,0 +1,45 @@
+package dbx
+
+import (
+	"testing"
+
+	"gitea.auvem.com/go-toolkit/dbx/internal/dbxshared"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDestName_MissingFieldWithoutModule(t *testing.T) {
+	type Foo struct {
+		Bar int
+	}
+
+	name := DestName(Foo{}, "Missing")
+	assert.Empty(t, name)
+}
+
+func TestDestName_ValidPath(t *testing.T) {
+	type Inner struct {
+		Value string
+	}
+	type Foo struct {
+		Inner Inner
+	}
+
+	name := DestName(Foo{}, "Inner", "Value")
+	assert.Equal(t, "Foo.Inner.Value", name)
+}
+
+func TestDialect_AfterModuleDB(t *testing.T) {
+	if dbxshared.DBModule != nil {
+		t.Skip("database module already initialized")
+	}
+
+	_ = ModuleDB(DialectPostgres, &DBConfig{
+		User:     "user",
+		Password: "pass",
+		URI:      "localhost:5432",
+		Name:     "test",
+		MaxConn:  1,
+	}, false)
+
+	assert.Equal(t, DialectPostgres, CurrentDialect())
+}