feat(i18n): add toast i18n with en/zh locale and plugin config support

- Add src/locales/ with en baseline and zh overrides (Partial<Record> fallback)
- Add src/shared/i18n.ts with initI18n/t/setLocale/getLocale (LANG env auto-detect)
- Add I18nConfigSchema with locale field to plugin config
- Internationalize 13 hardcoded strings in task-toast-manager
- Add 18 unit tests for i18n module
- Pin manager tests to en locale for determinism

src/locales/en.ts

@@ -0,0 +1,19 @@
+const locales = {
+  "toast.new_background_task": "New Background Task",
+  "toast.new_task_executed": "New Task Executed",
+  "toast.task_completed": "Task Completed",
+  "toast.task_completion_message": "\"{{description}}\" finished in {{duration}}",
+  "toast.task_completion_remaining": "Still running: {{running}} | Queued: {{queued}}",
+  "toast.status_queued": "Queued",
+  "toast.task_list_running": "Running ({{count}}):",
+  "toast.task_list_queued": "Queued ({{count}}):",
+  "toast.task_list_new": " ← NEW",
+  "toast.fallback_prefix": "[FALLBACK] Model: {{model}}{{suffix}}",
+  "toast.fallback_inherited": " (inherited from parent)",
+  "toast.fallback_system_default": " (system default fallback)",
+  "toast.fallback_runtime": " (runtime fallback)",
+  "toast.concurrency_info": " [{{total}}/{{limit}}]",
+} as const
+
+export type TranslationKey = keyof typeof locales
+export default locales

src/locales/index.ts

@@ -0,0 +1,12 @@
+import en, { type TranslationKey } from "./en"
+import zh from "./zh"
+
+export type { TranslationKey }
+export type SupportedLocale = "en" | "zh"
+export type LocaleMessages = Record<TranslationKey, string>
+
+type LocaleMap = Record<SupportedLocale, LocaleMessages>
+export const locales: LocaleMap = {
+  en,
+  zh,
+}

src/locales/zh.ts

@@ -0,0 +1,25 @@
+import en, { type TranslationKey } from "./en"
+
+const overrides: Partial<Record<TranslationKey, string>> = {
+  "toast.new_background_task": "新后台任务",
+  "toast.new_task_executed": "新任务已执行",
+  "toast.task_completed": "任务完成",
+  "toast.task_completion_message": "\"{{description}}\" 完成，耗时 {{duration}}",
+  "toast.task_completion_remaining": "仍在运行: {{running}} | 排队中: {{queued}}",
+  "toast.status_queued": "排队中",
+  "toast.task_list_running": "运行中 ({{count}}):",
+  "toast.task_list_queued": "排队中 ({{count}}):",
+  "toast.task_list_new": " ← 新任务",
+  "toast.fallback_prefix": "[回退] 模型: {{model}}{{suffix}}",
+  "toast.fallback_inherited": " (继承自父级)",
+  "toast.fallback_system_default": " (系统默认回退)",
+  "toast.fallback_runtime": " (运行时回退)",
+  "toast.concurrency_info": " [{{total}}/{{limit}}]",
+}
+
+const locales = {
+  ...en,
+  ...overrides,
+} satisfies Record<TranslationKey, string>
+
+export default locales