Handle SMSG_CHARACTER_LOGIN_FAILED (0x041) for AzerothCore/Playerbot compatibility

Previously this opcode was unrecognised and silently dropped, leaving the
client stuck in ENTERING_WORLD with no feedback when the server rejected a
login (duplicate session, world down, disabled race/class, etc.). Now we
decode the LoginFailureReason byte, reset state to CHAR_LIST_RECEIVED so
the player can retry, and surface a red error message on the character screen
via the new CharLoginFailCallback. Also adds isError colour support to
CharacterScreen::setStatus so failures show in red and successes in green.

include/game/opcode_table.hpp

@@ -47,6 +47,7 @@ enum class LogicalOpcode : uint16_t {
     SMSG_CHAR_CREATE,
     SMSG_CHAR_ENUM,
     SMSG_CHAR_DELETE,
+    SMSG_CHARACTER_LOGIN_FAILED,
     SMSG_PONG,
     SMSG_LOGIN_VERIFY_WORLD,
     SMSG_LOGIN_SETTIMESPEED,