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/online-store.ts

@@ -3,6 +3,7 @@
 import { create } from "zustand";
 import { CreateRoomOptions, MatchmakingOptions, getService } from "./online/service";
 import {
+  ChatMessage,
   Friend,
   FriendRequest,
   LeaderboardEntry,
@@ -35,11 +36,19 @@ interface OnlineStore {
   cancelMatchmaking: () => Promise<void>;
 
   loadLeaderboard: () => Promise<void>;
+
+  // chat
+  activeChatFriend: Friend | null;
+  chatMessages: ChatMessage[];
+  openChat: (friend: Friend) => Promise<void>;
+  sendChat: (text: string) => Promise<void>;
+  closeChat: () => void;
 }
 
 let roomUnsub: (() => void) | null = null;
 let mmUnsub: (() => void) | null = null;
 let friendUnsub: (() => void) | null = null;
+let chatUnsub: (() => void) | null = null;
 
 export const useOnlineStore = create<OnlineStore>((set, get) => ({
   friends: [],
@@ -128,4 +137,36 @@ export const useOnlineStore = create<OnlineStore>((set, get) => ({
     const leaderboard = await getService().getLeaderboard();
     set({ leaderboard });
   },
+
+  activeChatFriend: null,
+  chatMessages: [],
+
+  openChat: async (friend) => {
+    const svc = getService();
+    set({ activeChatFriend: friend, chatMessages: await svc.getMessages(friend.id) });
+    await svc.markRead(friend.id);
+    if (chatUnsub) chatUnsub();
+    chatUnsub = svc.onChat((friendId, msgs) => {
+      const active = get().activeChatFriend;
+      if (active && active.id === friendId) {
+        set({ chatMessages: msgs });
+        svc.markRead(friendId);
+      }
+    });
+  },
+
+  sendChat: async (text) => {
+    const friend = get().activeChatFriend;
+    if (!friend || !text.trim()) return;
+    await getService().sendMessage(friend.id, text);
+    set({ chatMessages: await getService().getMessages(friend.id) });
+  },
+
+  closeChat: () => {
+    if (chatUnsub) {
+      chatUnsub();
+      chatUnsub = null;
+    }
+    set({ activeChatFriend: null, chatMessages: [] });
+  },
 }));