Fix trainer system and add critical spell/quest opcodes

Trainer System Fixes:
- Fix CMSG_TRAINER_BUY_SPELL packet: remove incorrect trainerType field (12 bytes not 16)
- Correct spell state interpretation: 0=available, 1=unavailable, 2=known
- Add dynamic prerequisite re-evaluation in real-time as spells are learned
- Immediately update knownSpells on SMSG_TRAINER_BUY_SUCCEEDED
- Add "Show unavailable spells" checkbox filter to trainer window
- Override server state when prerequisites become met client-side

New Spell Opcodes:
- SMSG_SUPERCEDED_SPELL (0x12C): handle spell rank upgrades
- SMSG_SEND_UNLEARN_SPELLS (0x41F): handle bulk unlearning (respec/dual-spec)
- CMSG_TRAINER_LIST (0x1B0): trainer request opcode

Quest System:
- SMSG_QUESTUPDATE_COMPLETE (0x195): mark quests complete when objectives done
- Show "Quest Complete" message and enable turn-in UI

Detailed logging:
- SMSG_INITIAL_SPELLS now logs packet size and first 10 spell IDs
- Money values logged during trainer purchases
- Trainer spell states and prerequisites logged for debugging

This enables proper spell progression chains, spec changes, and quest completion
notifications matching retail WoW 3.3.5a behavior.

include/game/game_handler.hpp

@@ -495,6 +495,8 @@ public:
         std::string title;
         std::string objectives;
         bool complete = false;
+        // Objective kill counts: objectiveIndex -> (current, required)
+        std::unordered_map<uint32_t, std::pair<uint32_t, uint32_t>> killCounts;
     };
     const std::vector<QuestLogEntry>& getQuestLog() const { return questLog_; }
     void abandonQuest(uint32_t questId);
@@ -697,7 +699,9 @@ private:
     void handleCooldownEvent(network::Packet& packet);
     void handleAuraUpdate(network::Packet& packet, bool isAll);
     void handleLearnedSpell(network::Packet& packet);
+    void handleSupercededSpell(network::Packet& packet);
     void handleRemovedSpell(network::Packet& packet);
+    void handleUnlearnSpells(network::Packet& packet);
 
     // ---- Phase 4 handlers ----
     void handleGroupInvite(network::Packet& packet);