feat(i18n): add English localization with per-user language preference

app/i18n.py

@@ -33,6 +33,14 @@ _translations: dict[str, dict[str, str]] = {
     "dash.countries": {"zh": "国家/地区", "en": "Countries"},
     "dash.chart_sent": {"zh": "📤 寄出", "en": "📤 Sent"},
     "dash.chart_received": {"zh": "📬 收到", "en": "📬 Received"},
+    "dash.recent": {"zh": "最近动态", "en": "Recent activity"},
+    "dash.empty": {"zh": "暂无明信片", "en": "No postcards yet"},
+    "dash.welcome_title": {"zh": "欢迎使用星笺！", "en": "Welcome to Mailova!"},
+    "dash.welcome_hint": {"zh": "创建一个", "en": "Create a"},
+    "dash.welcome_hint2": {"zh": " 开始管理你的明信片", "en": " to start managing your postcards"},
+    "dash.today": {"zh": "今天", "en": "Today"},
+    "dash.yesterday": {"zh": "昨天", "en": "Yesterday"},
+    "dash.days_ago": {"zh": "天前", "en": " days ago"},
 
     # ── Profiles ──
     "profiles.title": {"zh": "Profile", "en": "Profiles"},
@@ -159,6 +167,7 @@ _translations: dict[str, dict[str, str]] = {
     "invites.max_uses": {"zh": "最大使用次数", "en": "Max uses"},
     "invites.expires_time": {"zh": "过期时间", "en": "Expiration"},
     "invites.registered_users": {"zh": "注册用户", "en": "Registered users"},
+    "invites.empty": {"zh": "暂无邀请码", "en": "No invite codes yet"},
 
     # ── Showcase (public) ──
     "showcase.title": {"zh": " 的明信片", "en": "'s postcards"},