refactor(cli): update auth.zig to use io.zig

Update auth.zig import from colors.zig to io.zig:
- colors.zig is now consolidated into io.zig
- Use io module directly for consistency

All tests pass.

cli/src/utils/auth.zig

@@ -1,7 +1,7 @@
 const std = @import("std");
 const Config = @import("../config.zig").Config;
 const ws = @import("../net/ws/client.zig");
-const colors = @import("colors.zig");
+const io = @import("io.zig");
 
 /// UserContext represents an authenticated user session
 pub const UserContext = struct {