Fix quest details parser, ImGui ID conflict, and gossip reopen guard

Quest details parser now reads all 6 choice + 4 reward item slots
(matching AzerothCore's fixed-size arrays) with bounds checking at
every step. Use loop index for quest ImGui IDs instead of questId to
avoid conflicts. Don't reopen gossip window while quest details are
showing.

src/game/game_handler.cpp

@@ -3623,6 +3623,7 @@ void GameHandler::handleLootRemoved(network::Packet& packet) {
 
 void GameHandler::handleGossipMessage(network::Packet& packet) {
     if (!GossipMessageParser::parse(packet, currentGossip)) return;
+    if (questDetailsOpen) return; // Don't reopen gossip while viewing quest
     gossipWindowOpen = true;
     vendorWindowOpen = false; // Close vendor if gossip opens
 }