Build fails with Go < 1.21 due to slices package dependency

[muthusanas]

Description

The build fails when using Go versions older than 1.21 because the codebase uses the `slices` package which was introduced in Go 1.21.

Error Message

internal/api/websocket.go:7:2: package slices is not in GOROOT (/usr/lib/go-1.18/src/slices)                                                                                                             

Location

• File: internal/api/websocket.go:52
• Usage: slices.ContainsFunc() for origin validation

Suggested Fix

Either:

1. Document the minimum Go version requirement (Go 1.21+) in README and go.mod
2. Replace slices.ContainsFunc() with a manual loop for backward compatibility