feat(ui): add i18n scaffolding

Adds a minimal i18n provider with locale preference support and migrates folder selection copy to message keys.

packages/ui/src/main.tsx

@@ -4,6 +4,7 @@ import { ThemeProvider } from "./lib/theme"
 import { ConfigProvider } from "./stores/preferences"
 import { InstanceConfigProvider } from "./stores/instance-config"
 import { runtimeEnv } from "./lib/runtime-env"
+import { I18nProvider } from "./lib/i18n"
 import "./index.css"
 import "@git-diff-view/solid/styles/diff-view-pure.css"
 
@@ -22,9 +23,11 @@ render(
   () => (
     <ConfigProvider>
       <InstanceConfigProvider>
-        <ThemeProvider>
-          <App />
-        </ThemeProvider>
+        <I18nProvider>
+          <ThemeProvider>
+            <App />
+          </ThemeProvider>
+        </I18nProvider>
       </InstanceConfigProvider>
     </ConfigProvider>
   ),