Add multi-expansion support with data-driven protocol layer

Replace hardcoded WotLK protocol constants with a data-driven architecture
supporting Classic 1.12.1, TBC 2.4.3, and WotLK 3.3.5a. Each expansion
has JSON profiles for opcodes, update fields, and DBC layouts, plus C++
polymorphic packet parsers for binary format differences (movement flags,
speed fields, transport data, spline format, char enum layout).

Key components:
- ExpansionRegistry: scans Data/expansions/*/expansion.json at startup
- OpcodeTable: logical enum <-> wire values loaded from JSON
- UpdateFieldTable: field indices loaded from JSON per expansion
- DBCLayout: schema-driven DBC field lookups replacing magic numbers
- PacketParsers: WotLK/TBC/Classic parsers with correct flag positions
- Multi-manifest AssetManager: layered manifests with priority ordering
- HDPackManager: overlay texture packs with expansion compatibility
- Auth screen expansion picker replacing hardcoded version dropdown

include/game/game_handler.hpp

@@ -2,6 +2,8 @@
 
 #include "game/world_packets.hpp"
 #include "game/character.hpp"
+#include "game/opcode_table.hpp"
+#include "game/update_field_table.hpp"
 #include "game/inventory.hpp"
 #include "game/spell_defines.hpp"
 #include "game/group_defines.hpp"
@@ -23,6 +25,7 @@ namespace wowee::game {
     class TransportManager;
     class WardenCrypto;
     class WardenModuleManager;
+    class PacketParsers;
 }
 
 namespace wowee {
@@ -109,6 +112,14 @@ public:
     GameHandler();
     ~GameHandler();
 
+    /** Access the active opcode table (wire ↔ logical mapping). */
+    const OpcodeTable& getOpcodeTable() const { return opcodeTable_; }
+    OpcodeTable& getOpcodeTable() { return opcodeTable_; }
+    const UpdateFieldTable& getUpdateFieldTable() const { return updateFieldTable_; }
+    UpdateFieldTable& getUpdateFieldTable() { return updateFieldTable_; }
+    PacketParsers* getPacketParsers() { return packetParsers_.get(); }
+    void setPacketParsers(std::unique_ptr<PacketParsers> parsers);
+
     /**
      * Connect to world server
      *
@@ -927,6 +938,15 @@ private:
                                 float localOrientation);
     void clearTransportAttachment(uint64_t childGuid);
 
+    // Opcode translation table (expansion-specific wire ↔ logical mapping)
+    OpcodeTable opcodeTable_;
+
+    // Update field table (expansion-specific field index mapping)
+    UpdateFieldTable updateFieldTable_;
+
+    // Packet parsers (expansion-specific binary format handling)
+    std::unique_ptr<PacketParsers> packetParsers_;
+
     // Network
     std::unique_ptr<network::WorldSocket> socket;
 
@@ -1210,7 +1230,6 @@ private:
     std::unordered_map<uint32_t, uint32_t> spellToSkillLine_;      // spellID -> skillLineID
     bool skillLineDbcLoaded_ = false;
     bool skillLineAbilityLoaded_ = false;
-    static constexpr uint16_t PLAYER_EXPLORED_ZONES_START = 1041;  // 3.3.5a UpdateFields
     static constexpr size_t PLAYER_EXPLORED_ZONES_COUNT = 128;
     std::vector<uint32_t> playerExploredZones_ =
         std::vector<uint32_t>(PLAYER_EXPLORED_ZONES_COUNT, 0u);