Add friend chat; replace betting wording (شرط) with entry coins

- Friend-to-friend chat outside the game (ChatScreen) with mock replies,
  per-friend history, unread tracking; chat button on each friend row
- OnlineService + mock + online-store extended with chat (list/get/send/markRead)
- Reframe gambling term: "شرط"/"Stake" -> "سکه ورودی"/"Entry coins";
  free entry labeled رایگان/Free

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/i18n.tsx

@@ -87,6 +87,13 @@ const fa: Dict = {
   "common.soon": "به‌زودی",
   "common.copy": "کپی",
   "common.copied": "کپی شد",
+  "common.free": "رایگان",
+
+  "chat.title": "گفتگو",
+  "chat.placeholder": "پیام بنویسید…",
+  "chat.send": "ارسال",
+  "chat.empty": "گفتگو را شروع کنید",
+  "friends.message": "پیام",
 
   "profile.title": "پروفایل",
   "profile.stats": "آمار",
@@ -128,7 +135,7 @@ const fa: Dict = {
   "room.empty": "خالی",
   "room.waiting": "در انتظار…",
   "room.start": "شروع بازی",
-  "room.stake": "شرط",
+  "room.stake": "سکه ورودی",
   "room.leave": "ترک اتاق",
   "room.pickFriend": "یک دوست را انتخاب کنید",
 
@@ -265,6 +272,13 @@ const en: Dict = {
   "common.soon": "Coming soon",
   "common.copy": "Copy",
   "common.copied": "Copied",
+  "common.free": "Free",
+
+  "chat.title": "Chat",
+  "chat.placeholder": "Type a message…",
+  "chat.send": "Send",
+  "chat.empty": "Start the conversation",
+  "friends.message": "Message",
 
   "profile.title": "Profile",
   "profile.stats": "Stats",
@@ -306,7 +320,7 @@ const en: Dict = {
   "room.empty": "Empty",
   "room.waiting": "Waiting…",
   "room.start": "Start game",
-  "room.stake": "Stake",
+  "room.stake": "Entry coins",
   "room.leave": "Leave room",
   "room.pickFriend": "Pick a friend",