feat: P0d 会员定价页重构 — 用量可视化 + 方案对比

- 三栏定价卡片（免费/月卡/年卡），参考 opencode Go 页面风格
- 日配额用量进度条
- 功能对比表（沙盒/模型/提示词/课程/广告）
- 当前方案标记 + 最受欢迎标记
- useT 全量翻译
- 补充中/英 30+ 定价相关翻译 key

frontend/src/i18n/locales/en.ts

@@ -97,6 +97,38 @@ const en: Translations = {
     orderHistory: 'Order History',
     noOrders: 'No orders yet',
     processing: 'Processing...',
+    planFree: 'Free',
+    planMonthly: 'Monthly',
+    planYearly: 'Yearly',
+    priceMonthly: '¥29.9',
+    priceYearly: '¥199',
+    perMonth: '/mo',
+    perYear: '/yr',
+    popular: 'Most Popular',
+    featureSandbox: 'AI Sandbox',
+    featureSandboxFree: '10/day',
+    featureSandboxPro: '100/day',
+    featureSandboxUnlimited: 'Unlimited',
+    featureModels: 'Models',
+    featureModelsFree: '1 model',
+    featureModelsPro: '2 models',
+    featureModelsPremium: 'All models',
+    featurePrompts: 'Prompts',
+    featurePromptsFree: 'Basic',
+    featurePromptsPro: 'All',
+    featurePromptsPremium: 'All + Exclusive',
+    featureCourses: 'Courses',
+    featureCoursesFree: 'Some free',
+    featureCoursesPro: 'All',
+    featureCoursesPremium: 'All',
+    featureAds: 'Ads',
+    featureAdsFree: 'Yes',
+    featureAdsPro: 'Ad-free',
+    featureAdsPremium: 'Ad-free',
+    dailyQuota: 'Daily Quota Usage',
+    used: '{n} used',
+    subscribe: 'Subscribe',
+    currentPlan_badge: 'Current Plan',
   },
   compare: {
     title: 'Compare Lab',