Pre/Post hooks safety controls #100

Summary
Hooks run with shell=true which is powerful but may be risky by default. Provide safety controls.

Proposed changes

• Add --no-hooks flag to skip all hooks.
• Add confirmation prompt when hooks will run unless --yes or --non-interactive is set.
• Optional allowlist file (e.g., .struct-hooks-allowlist) to restrict executable commands.

Files

• struct_module/commands/generate.py (_run_hooks and execute)
• docs/hooks.md

Acceptance criteria

• Users can skip hooks or run non-interactively without prompts.
• Allowlist behavior documented and covered by tests.