feat: encrypted secrets, runner config, clack/hono/valibot refactor
- Add encrypted secrets system (X25519 + XSalsa20-Poly1305)
- CLI: runner init/info, secrets set/list/delete commands
- Runner: config file support, access control, resource limits
- Refactor CLI to use @clack/prompts
- Refactor runner to use Hono
- Add valibot for input validation
- Add resource limits (memory, timeout) to sandbox