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/game/opcode_table.hpp

@@ -351,6 +351,19 @@ enum class LogicalOpcode : uint16_t {
     SMSG_ARENA_ERROR,
     MSG_INSPECT_ARENA_TEAMS,
 
+    // ---- Emotes ----
+    CMSG_EMOTE,
+    SMSG_EMOTE,
+    CMSG_TEXT_EMOTE,
+    SMSG_TEXT_EMOTE,
+
+    // ---- Channels ----
+    CMSG_JOIN_CHANNEL,
+    CMSG_LEAVE_CHANNEL,
+    SMSG_CHANNEL_NOTIFY,
+    CMSG_CHANNEL_LIST,
+    SMSG_CHANNEL_LIST,
+
     // Sentinel
     COUNT
 };