feat: add cooldown tracker panel showing all active spell cooldowns

A new opt-in panel (Settings > Interface > Show Cooldown Tracker) lists
all spells currently on cooldown, sorted longest-to-shortest, with
spell icons and color-coded remaining time (red>30s, orange>10s,
yellow>5s, green<5s). Adds getSpellCooldowns() accessor to GameHandler.
Setting persists to ~/.wowee/settings.cfg.

include/game/game_handler.hpp

@@ -983,6 +983,7 @@ public:
 
     // Cooldowns
     float getSpellCooldown(uint32_t spellId) const;
+    const std::unordered_map<uint32_t, float>& getSpellCooldowns() const { return spellCooldowns; }
 
     // Player GUID
     uint64_t getPlayerGuid() const { return playerGuid; }