Playerbot: BotGear addon — register the PBC addon-message prefix

The client only fires CHAT_MSG_ADDON events for prefixes registered via
RegisterAddonMessagePrefix. BotGear never registered 'PBC' (PlayerbotControl
does), so the server's GEAR_BAGS_RESP / GEAR_EQUIP_RESP replies were dropped
client-side and the panel stayed blank even though the round-trip reached the
server. Register the prefix on PLAYER_LOGIN.

src/modules/PlayerbotV2/Addon/BotGear/BotGear.lua

@@ -374,6 +374,20 @@ local function BuildFrame()
     refresh:SetScript("OnClick", RefreshTarget)
 end
 
+-- Register the PBC prefix so the client delivers CHAT_MSG_ADDON events for
+-- the server's replies — without this, GEAR_BAGS_RESP/GEAR_EQUIP_RESP are
+-- silently dropped client-side and the panel stays blank.
+local init = CreateFrame("Frame")
+init:RegisterEvent("PLAYER_LOGIN")
+init:SetScript("OnEvent", function()
+    if C_ChatInfo and C_ChatInfo.RegisterAddonMessagePrefix then
+        C_ChatInfo.RegisterAddonMessagePrefix(PREFIX)
+    elseif RegisterAddonMessagePrefix then
+        RegisterAddonMessagePrefix(PREFIX)
+    end
+    init:UnregisterAllEvents()
+end)
+
 -- Inbound PBC messages
 local f = CreateFrame("Frame")
 f:RegisterEvent("CHAT_MSG_ADDON")