refactor(game): split GameHandler into domain handlers

Extract domain-specific logic from the monolithic GameHandler into
dedicated handler classes, each owning its own opcode registration,
state, and packet parsing:

- CombatHandler: combat, XP, kill, PvP, loot roll (~26 methods)
- SpellHandler: spells, auras, pet stable, talent (~3+ methods)
- SocialHandler: friends, guild, groups, BG, RAF, PvP AFK (~14+ methods)
- ChatHandler: chat messages, channels, GM tickets, server messages,
               defense/area-trigger messages (~7+ methods)
- InventoryHandler: items, trade, loot, mail, vendor, equipment sets,
                    read item (~3+ methods)
- QuestHandler: gossip, quests, completed quest response (~5+ methods)
- MovementHandler: movement, follow, transport (~2 methods)
- WardenHandler: Warden anti-cheat module

Each handler registers its own dispatch table entries via
registerOpcodes(DispatchTable&), called from
GameHandler::registerOpcodeHandlers(). GameHandler retains core
orchestration: auth/session handshake, update-object parsing,
opcode routing, and cross-handler coordination.

game_handler.cpp reduced from ~10,188 to ~9,432 lines.

Also add a POST_BUILD CMake step to symlink Data/ next to the
executable so expansion profiles and opcode tables are found at
runtime when running from build/bin/.

include/game/game_utils.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "game/expansion_profile.hpp"
+#include "core/application.hpp"
+
+namespace wowee {
+namespace game {
+
+inline bool isActiveExpansion(const char* expansionId) {
+    auto& app = core::Application::getInstance();
+    auto* registry = app.getExpansionRegistry();
+    if (!registry) return false;
+    auto* profile = registry->getActive();
+    if (!profile) return false;
+    return profile->id == expansionId;
+}
+
+inline bool isClassicLikeExpansion() {
+    return isActiveExpansion("classic") || isActiveExpansion("turtle");
+}
+
+inline bool isPreWotlk() {
+    return isClassicLikeExpansion() || isActiveExpansion("tbc");
+}
+
+} // namespace game
+} // namespace wowee