feat: add melee swing timer bar to player frame during auto-attack

Shows a thin progress bar below the player health/power bars whenever
the player is auto-attacking. The bar fills from the last swing timestamp
to the next expected swing based on the main-hand weapon's delay (from
ItemQueryResponseData::delayMs). Falls back to 2.0s for unarmed. Turns
gold and shows "Swing!" when the timer is complete to signal readiness.
Hides when not auto-attacking.

src/game/game_handler.cpp

@@ -14328,8 +14328,11 @@ void GameHandler::handleAttackerStateUpdate(network::Packet& packet) {
     bool isPlayerTarget = (data.targetGuid == playerGuid);
     if (!isPlayerAttacker && !isPlayerTarget) return;  // Not our combat
 
-    if (isPlayerAttacker && meleeSwingCallback_) {
-        meleeSwingCallback_();
+    if (isPlayerAttacker) {
+        lastMeleeSwingMs_ = static_cast<uint64_t>(
+            std::chrono::duration_cast<std::chrono::milliseconds>(
+                std::chrono::system_clock::now().time_since_epoch()).count());
+        if (meleeSwingCallback_) meleeSwingCallback_();
     }
     if (!isPlayerAttacker && npcSwingCallback_) {
         npcSwingCallback_(data.attackerGuid);