Add chat tabs, networked text emotes, channel system, and chat bubbles

Chat tabs filter messages into General/Combat/Whispers/Trade tabs. Text
emotes now send CMSG_TEXT_EMOTE to server and display incoming emotes
from other players. Channel system auto-joins General/Trade on login with
/join, /leave, and /1-/9 shortcuts. Chat bubbles render as ImGui overlays
above entities for SAY/YELL messages with fade-out animation.

include/rendering/renderer.hpp

@@ -125,6 +125,7 @@ public:
     void cancelEmote();
     bool isEmoteActive() const { return emoteActive; }
     static std::string getEmoteText(const std::string& emoteName, const std::string* targetName = nullptr);
+    static uint32_t getEmoteDbcId(const std::string& emoteName);
 
     // Targeting support
     void setTargetPosition(const glm::vec3* pos);