Fix --no-input hang when stdin is a socket or non-pipe fd

[harriiinnii]

Problem

jira issue create --no-input (and jira issue comment add --no-input) hangs indefinitely when the process is invoked from a subprocess context where stdin is a Unix socket pair, a character device, or any other non-pipe, non-file fd.

StdinHasData() returned true for any non-terminal fd:

func StdinHasData() bool {
    return !term.IsTerminal(int(os.Stdin.Fd()))
}

This caused ReadFile("") to call io.ReadAll(os.Stdin) and block forever, because socket pairs only return EOF when the peer explicitly shuts down the write half — which automation tools typically do not do.

Fix

Narrow the StdinHasData() check so it returns true only when stdin is a named pipe (os.ModeNamedPipe) or a regular file (mode.IsRegular()). This matches the actual intent — "did the caller pipe or redirect data?" — and leaves sockets, character devices, and other special files returning false.

func StdinHasData() bool {
    if term.IsTerminal(int(os.Stdin.Fd())) {
        return false
    }
    fi, err := os.Stdin.Stat()
    if err != nil {
        return false
    }
    mode := fi.Mode()
    return mode&os.ModeNamedPipe != 0 || mode.IsRegular()
}

Both common use cases continue to work as before:

• echo "body" | jira issue create ... — pipe, returns true
• jira issue create ... < body.txt — regular file, returns true

Fixes #948
Fixes #984