Add automation-friendly flags (--yes, --noconfirm)

[Aurelian-Shuttleworth]

Problem

gcalcli defaults to interactive ncurses-style prompts for destructive actions (delete, import). This behavior breaks unattended scripts and cron jobs, causing pipelines to hang indefinitely waiting for user input that never comes.

Solution

Implement automation-friendly flags to enable true headless operation.

• --noconfirm / --yes: Bypass confirmation prompts for delete/import operations.
• --noprompt: Fail fast or use defaults instead of entering interactive wizard modes for missing arguments.
• Idempotency: Ensure commands return appropriate exit codes (0 for success, non-zero for failure) to allow proper error handling in shell scripts and orchestration tools.