fix: restore full color depth for hex color codes (§#RRGGBB)

After the dialog system PR (#3143), ResolveHexColors in ClassicConsoleBackend
mapped every §#RRGGBB hex color to the nearest of 16 standard Minecraft colors
via NearestMcColor. This meant all server-sent hex colors were downgraded to
4-bit ANSI regardless of the user's ConsoleColorMode setting.

Replaced the nearest-color lookup with ColorHelper.GetColorEscapeCode, which
generates the right output for each mode: 24-bit ANSI in vt100_24bit mode, 8-bit
in vt100_8bit, 4-bit in vt100_4bit, ConsoleColor in legacy_4bit.

Fixes #3146.

MinecraftClient/ClassicConsoleBackend.cs

@@ -64,7 +64,7 @@ namespace MinecraftClient
                 byte r = (byte)((HexVal(hex[0]) << 4) | HexVal(hex[1]));
                 byte g = (byte)((HexVal(hex[2]) << 4) | HexVal(hex[3]));
                 byte b = (byte)((HexVal(hex[4]) << 4) | HexVal(hex[5]));
-                return $"§{NearestMcColor(r, g, b)}";
+                return ColorHelper.GetColorEscapeCode(r, g, b, foreground: true);
             });
         }