feat: add duel countdown overlay (3-2-1-Fight!)

Parse SMSG_DUEL_COUNTDOWN to get the countdown duration, track the
start time, and render a large centered countdown overlay. Numbers
display in pulsing gold; transitions to pulsing red 'Fight!' for the
last 0.5 seconds. Countdown clears on SMSG_DUEL_COMPLETE.

include/game/game_handler.hpp

@@ -1035,6 +1035,14 @@ public:
     const std::string& getDuelChallengerName() const { return duelChallengerName_; }
     void acceptDuel();
     // forfeitDuel() already declared at line ~399
+    // Returns remaining duel countdown seconds, or 0 if no active countdown
+    float getDuelCountdownRemaining() const {
+        if (duelCountdownMs_ == 0) return 0.0f;
+        auto elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(
+            std::chrono::steady_clock::now() - duelCountdownStartedAt_).count();
+        float rem = (static_cast<float>(duelCountdownMs_) - static_cast<float>(elapsed)) / 1000.0f;
+        return rem > 0.0f ? rem : 0.0f;
+    }
 
     // ---- Instance lockouts ----
     struct InstanceLockout {
@@ -2251,6 +2259,8 @@ private:
     uint64_t duelChallengerGuid_= 0;
     uint64_t duelFlagGuid_      = 0;
     std::string duelChallengerName_;
+    uint32_t duelCountdownMs_   = 0;   // 0 = no active countdown
+    std::chrono::steady_clock::time_point duelCountdownStartedAt_{};
 
     // ---- Guild state ----
     std::string guildName_;

include/ui/game_screen.hpp

@@ -293,6 +293,7 @@ private:
     void renderQuestCompleteToasts(float deltaTime);
     void renderGroupInvitePopup(game::GameHandler& gameHandler);
     void renderDuelRequestPopup(game::GameHandler& gameHandler);
+    void renderDuelCountdown(game::GameHandler& gameHandler);
     void renderLootRollPopup(game::GameHandler& gameHandler);
     void renderTradeRequestPopup(game::GameHandler& gameHandler);
     void renderTradeWindow(game::GameHandler& gameHandler);

src/game/game_handler.cpp

@@ -3214,9 +3214,16 @@ void GameHandler::handlePacket(network::Packet& packet) {
         case Opcode::SMSG_DUEL_INBOUNDS:
             // Re-entered the duel area; no special action needed.
             break;
-        case Opcode::SMSG_DUEL_COUNTDOWN:
-            // Countdown timer — no action needed; server also sends UNIT_FIELD_FLAGS update.
+        case Opcode::SMSG_DUEL_COUNTDOWN: {
+            // uint32 countdown in milliseconds (typically 3000 ms)
+            if (packet.getSize() - packet.getReadPos() >= 4) {
+                uint32_t ms = packet.readUInt32();
+                duelCountdownMs_        = (ms > 0 && ms <= 30000) ? ms : 3000;
+                duelCountdownStartedAt_ = std::chrono::steady_clock::now();
+                LOG_INFO("SMSG_DUEL_COUNTDOWN: ", duelCountdownMs_, " ms");
+            }
             break;
+        }
         case Opcode::SMSG_PARTYKILLLOG: {
             // uint64 killerGuid + uint64 victimGuid
             if (packet.getSize() - packet.getReadPos() < 16) break;
@@ -10472,6 +10479,7 @@ void GameHandler::handleDuelComplete(network::Packet& packet) {
     uint8_t started = packet.readUInt8();
     // started=1: duel began, started=0: duel was cancelled before starting
     pendingDuelRequest_ = false;
+    duelCountdownMs_    = 0; // clear countdown once duel is resolved
     if (!started) {
         addSystemChatMessage("The duel was cancelled.");
     }

src/ui/game_screen.cpp

@@ -482,6 +482,7 @@ void GameScreen::render(game::GameHandler& gameHandler) {
     renderBossFrames(gameHandler);
     renderGroupInvitePopup(gameHandler);
     renderDuelRequestPopup(gameHandler);
+    renderDuelCountdown(gameHandler);
     renderLootRollPopup(gameHandler);
     renderTradeRequestPopup(gameHandler);
     renderTradeWindow(gameHandler);
@@ -7488,6 +7489,47 @@ void GameScreen::renderDuelRequestPopup(game::GameHandler& gameHandler) {
     ImGui::End();
 }
 
+void GameScreen::renderDuelCountdown(game::GameHandler& gameHandler) {
+    float remaining = gameHandler.getDuelCountdownRemaining();
+    if (remaining <= 0.0f) return;
+
+    ImVec2 displaySize = ImGui::GetIO().DisplaySize;
+    float screenW = displaySize.x > 0.0f ? displaySize.x : 1280.0f;
+    float screenH = displaySize.y > 0.0f ? displaySize.y : 720.0f;
+
+    auto* dl = ImGui::GetForegroundDrawList();
+    ImFont* font = ImGui::GetFont();
+    float fontSize = ImGui::GetFontSize();
+
+    // Show integer countdown or "Fight!" when under 0.5s
+    char buf[32];
+    if (remaining > 0.5f) {
+        snprintf(buf, sizeof(buf), "%d", static_cast<int>(std::ceil(remaining)));
+    } else {
+        snprintf(buf, sizeof(buf), "Fight!");
+    }
+
+    // Large font by scaling — use 4x font size for dramatic effect
+    float scale = 4.0f;
+    float scaledSize = fontSize * scale;
+    ImVec2 textSz = font->CalcTextSizeA(scaledSize, FLT_MAX, 0.0f, buf);
+    float tx = (screenW - textSz.x) * 0.5f;
+    float ty = screenH * 0.35f - textSz.y * 0.5f;
+
+    // Pulsing alpha: fades in and out per second
+    float pulse = 0.75f + 0.25f * std::sin(static_cast<float>(ImGui::GetTime()) * 6.28f);
+    uint8_t alpha = static_cast<uint8_t>(255 * pulse);
+
+    // Color: golden countdown, red "Fight!"
+    ImU32 color = (remaining > 0.5f)
+        ? IM_COL32(255, 200, 50, alpha)
+        : IM_COL32(255, 60, 60, alpha);
+
+    // Drop shadow
+    dl->AddText(font, scaledSize, ImVec2(tx + 2.0f, ty + 2.0f), IM_COL32(0, 0, 0, alpha / 2), buf);
+    dl->AddText(font, scaledSize, ImVec2(tx, ty), color, buf);
+}
+
 void GameScreen::renderItemTextWindow(game::GameHandler& gameHandler) {
     if (!gameHandler.isItemTextOpen()) return;