[ax] Do not prompt or auto-create config on non-TTY

[TomasVotruba]

Why

Running rector process with no rector.php in a non-interactive context (piped, CI, an agent) currently:

• prints the interactive prompt No "rector.php" config found. Should we generate it for you? [yes]: into the output, then
• auto-answers the default yes and silently writes a rector.php into the project - a file the caller never asked for.

Symfony still treats a closed STDIN as interactive here, so the prompt is emitted and defaulted rather than skipped. For an agent this is a surprising side effect plus confusing prompt noise (and a hang risk when stdin is a pty with no human to answer).

What

Guard the prompt on a non-TTY STDIN: emit a clear, actionable message and return - no prompt, no unrequested file.

if (! (defined('STDIN') && stream_isatty(STDIN))) {
    $this->symfonyStyle->warning(sprintf(
        'No "%s" config found. Create one, or pass "--config <path>".',
        RectorConfigsResolver::DEFAULT_CONFIG_FILE
    ));
    return;
}

• Agent / pipe / CI: clear warning, no prompt, no rector.php written; the run falls through to the existing "no rules" handling.
• Human terminal: unchanged - prompt and generate as before.
• Same stream_isatty signal used in [ax] Disable progress bar when output is not a TTY #8444 / [ax] Never emit ANSI when output is not a TTY, even with --ansi #8453 (STDIN here, since the prompt reads stdin).

Trade-off: this drops the convenience of auto-scaffolding a config in non-interactive contexts. That silent write is the bug being fixed.

Verification

rector process src --dry-run < /dev/null in a dir with no config:

• before: prompt printed, rector.php created
• after: [WARNING] No "rector.php" config found. Create one, or pass "--config <path>.", no file created

Env-dependent (reads the real STDIN stream), so verified via the CLI rather than a unit test.