full non-interactive mode: eliminate all tty prompts when flags are provided

[yigitkonur]

problem

several commands still prompt for interactive input even when all required flags are provided. this breaks ci/cd pipelines, scripts, and ai agent automation.

specific commands that prompt unnecessarily:

• railway add --database mysql — prompts "what do you need?" even though --database is explicit
• railway add --image <img> -s <name> — prompts "enter a variable" with no way to skip
• railway down — prompts for confirmation with no --yes flag support

real-world scenario

building an automated deployment script that provisions a full stack (mysql + redis + backend + frontend). every railway add call hangs waiting for tty input despite having all flags. the workaround is piping /dev/null or < /dev/null which sometimes works, sometimes doesn't.

proposed solution

1. when all required params are provided via flags, skip interactive prompts entirely
2. add --yes / -y flag to all destructive commands (down, delete, etc.)
3. detect non-tty environments and error with a clear message instead of hanging

related

• Allow to create service from CLI without any input #799 — create service without input (open, same root cause)
• Using the CLI in a CI/CD environment to set the railway environment variables #574 — ci/cd environment variable issues (closed)
• Cli Timeout in CI environment when setting variables. #655 — cli timeout in ci (open, likely related to hanging prompts)