feat(i18n): add Lingui runtime and development tooling

- add SSR-safe I18nProvider, Translate, locale hooks, catalog activation, and typed runtime APIs

- add consumer-owned Lingui configuration helpers and a CLI for locale creation, extraction, compilation, and project discovery

- add catalog read/write services plus a Vite development API plugin scoped to each consuming application

- add the portal-based I18nDevtool, message editor, dark-theme tracking, and standalone Message Studio

- document the consumer workflow and cover runtime, configuration, catalog, CLI, and Devtool behavior with tests

packages/i18n/src/devtool/message-panel.test.tsx

@@ -0,0 +1,60 @@
+// @vitest-environment jsdom
+
+import * as React from "react"
+import { fireEvent, render, screen, waitFor } from "@testing-library/react"
+import { describe, expect, it, vi } from "vitest"
+
+import { MessagePanel } from "./message-panel"
+import type { DevtoolMessage, MessageRepository } from "./types"
+
+const message: DevtoolMessage = {
+  catalog: "messages",
+  comments: ["Navigation title"],
+  id: "navigation.home",
+  missing: true,
+  obsolete: false,
+  origins: [{ file: "src/navigation.tsx", line: 12 }],
+  source: "Home",
+  translation: "",
+}
+
+describe("MessagePanel", () => {
+  it("loads, filters, and saves messages through the repository", async () => {
+    const updateMessage = vi.fn(async (input) => ({
+      ...message,
+      missing: false,
+      translation: input.translation,
+    }))
+    const repository: MessageRepository = {
+      getMessages: vi.fn(async () => [message]),
+      updateMessage,
+    }
+
+    render(<MessagePanel locale="zh-Hans" repository={repository} />)
+
+    expect(await screen.findByText("navigation.home")).toBeTruthy()
+
+    const textarea = screen.getByLabelText(
+      "navigation.home translation for zh-Hans"
+    )
+    fireEvent.change(textarea, { target: { value: "首页" } })
+    fireEvent.click(screen.getByRole("button", { name: "Save" }))
+
+    await waitFor(() => {
+      expect(updateMessage).toHaveBeenCalledWith({
+        catalog: "messages",
+        id: "navigation.home",
+        locale: "zh-Hans",
+        translation: "首页",
+      })
+    })
+    expect(await screen.findByText("Saved")).toBeTruthy()
+
+    fireEvent.change(screen.getByPlaceholderText("Search messages"), {
+      target: { value: "does not exist" },
+    })
+    expect(
+      screen.getByText("No messages match the current filters.")
+    ).toBeTruthy()
+  })
+})