feat(i18n): expose localized text runtime primitive

Add a DOM-free LocalizedText component for MessageDescriptor values and export it from the runtime entry point.\n\nAlso expose provider detection so packages with a standalone fallback provider can avoid invoking Lingui hooks outside a provider. Cover localized rendering without an extra wrapper node.

packages/i18n/src/runtime/localized-text.tsx

@@ -0,0 +1,11 @@
+import { useMessage } from "./hooks"
+import type { MessageDescriptor } from "./types"
+
+export interface LocalizedTextProps {
+  message: MessageDescriptor
+}
+
+/** Renders a message descriptor as localized text without adding a DOM node. */
+export function LocalizedText({ message }: LocalizedTextProps) {
+  return useMessage(message)
+}