Fix missing os and strings imports in unified server (#3599)

Lint CI was failing because `internal/server/unified.go` used
`os.Getenv` and `strings.TrimSpace` without importing the corresponding
packages.

## Change

Added missing stdlib imports to `internal/server/unified.go`:

```go
import (
    ...
    "os"
    "strings"
    ...
)
```

Author: lpcox

internal/server/unified.go

@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"os"
+	"strings"
 	"sync"
 	"time"