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/lib/i18n/index.tsx

@@ -0,0 +1,104 @@
+import { createContext, createMemo, createSignal, onMount, useContext } from "solid-js"
+import type { ParentComponent } from "solid-js"
+import { useConfig } from "../../stores/preferences"
+import { enMessages } from "./messages/en"
+
+type Messages = Record<string, string>
+
+export type Locale = "en"
+
+const SUPPORTED_LOCALES: readonly Locale[] = ["en"] as const
+
+const messagesByLocale: Record<Locale, Messages> = {
+  en: enMessages,
+}
+
+function normalizeLocaleTag(value: string): string {
+  return value.trim().replace(/_/g, "-")
+}
+
+function matchSupportedLocale(value: string | undefined): Locale | null {
+  if (!value) return null
+
+  const normalized = normalizeLocaleTag(value)
+  const lower = normalized.toLowerCase()
+  const supportedLower = new Map(SUPPORTED_LOCALES.map((locale) => [locale.toLowerCase(), locale]))
+  const exact = supportedLower.get(lower)
+  if (exact) return exact
+
+  const base = lower.split("-")[0]
+  if (!base) return null
+  const baseMatch = supportedLower.get(base)
+  return baseMatch ?? null
+}
+
+function detectNavigatorLocale(): Locale | null {
+  if (typeof navigator === "undefined") return null
+
+  const candidates = Array.isArray(navigator.languages) && navigator.languages.length > 0
+    ? navigator.languages
+    : navigator.language
+      ? [navigator.language]
+      : []
+
+  for (const candidate of candidates) {
+    const match = matchSupportedLocale(candidate)
+    if (match) return match
+  }
+
+  return null
+}
+
+function interpolate(template: string, params?: Record<string, unknown>): string {
+  if (!params) return template
+  return template.replace(/\{(\w+)\}/g, (_match, key: string) => {
+    const value = params[key]
+    return value === undefined || value === null ? "" : String(value)
+  })
+}
+
+export interface I18nContextValue {
+  locale: () => Locale
+  t: (key: string, params?: Record<string, unknown>) => string
+}
+
+const I18nContext = createContext<I18nContextValue>()
+
+export const I18nProvider: ParentComponent = (props) => {
+  const { preferences } = useConfig()
+  const [detectedLocale, setDetectedLocale] = createSignal<Locale>("en")
+
+  onMount(() => {
+    const detected = detectNavigatorLocale()
+    if (detected) setDetectedLocale(detected)
+  })
+
+  const locale = createMemo<Locale>(() => {
+    const configured = matchSupportedLocale(preferences().locale)
+    return configured ?? detectedLocale() ?? "en"
+  })
+
+  const messages = createMemo<Messages>(() => messagesByLocale[locale()])
+
+  function t(key: string, params?: Record<string, unknown>): string {
+    const current = messages()[key]
+    const fallback = enMessages[key as keyof typeof enMessages]
+    const template = current ?? fallback ?? key
+    return interpolate(template, params)
+  }
+
+  const value: I18nContextValue = {
+    locale,
+    t,
+  }
+
+  return <I18nContext.Provider value={value}>{props.children}</I18nContext.Provider>
+}
+
+export function useI18n(): I18nContextValue {
+  const context = useContext(I18nContext)
+  if (!context) {
+    throw new Error("useI18n must be used within I18nProvider")
+  }
+  return context
+}

packages/ui/src/lib/i18n/messages/en.ts

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+export const enMessages = {
+  "folderSelection.logoAlt": "CodeNomad logo",
+  "folderSelection.tagline": "Select a folder to start coding with AI",
+
+  "folderSelection.links.github": "CodeNomad GitHub",
+  "folderSelection.links.githubStars": "CodeNomad GitHub Stars",
+  "folderSelection.links.discord": "CodeNomad Discord",
+
+  "folderSelection.empty.title": "No Recent Folders",
+  "folderSelection.empty.description": "Browse for a folder to get started",
+
+  "folderSelection.recent.title": "Recent Folders",
+  "folderSelection.recent.subtitle.one": "{count} folder available",
+  "folderSelection.recent.subtitle.other": "{count} folders available",
+  "folderSelection.recent.remove": "Remove from recent",
+
+  "folderSelection.browse.title": "Browse for Folder",
+  "folderSelection.browse.subtitle": "Select any folder on your computer",
+  "folderSelection.browse.button": "Browse Folders",
+  "folderSelection.browse.buttonOpening": "Opening...",
+
+  "folderSelection.advancedSettings": "Advanced Settings",
+
+  "folderSelection.hints.navigate": "Navigate",
+  "folderSelection.hints.select": "Select",
+  "folderSelection.hints.remove": "Remove",
+  "folderSelection.hints.browse": "Browse",
+
+  "folderSelection.loading.title": "Starting instance...",
+  "folderSelection.loading.subtitle": "Hang tight while we prepare your workspace.",
+
+  "folderSelection.dialog.title": "Select Workspace",
+  "folderSelection.dialog.description": "Select workspace to start coding.",
+
+  "time.relative.justNow": "just now",
+  "time.relative.daysAgoShort": "{count}d ago",
+  "time.relative.hoursAgoShort": "{count}h ago",
+  "time.relative.minutesAgoShort": "{count}m ago",
+} as const