* feat(sandbox): support sandbox and skill version entrypoint scripts

* refactor(sandbox): preserve sandbox entrypoint when disabled and simplify deployment marker

* refactor(sandbox): migrate sandbox initialization locking to Redis lease

* refactor(sandbox): split sandbox sub-module and support after-entrypoint

* refactor(sandbox): enforce strict Redis lease with auto-renewal

* refactor(sandbox): support platform bootstrap callback

* docs(agent): Agent V2 settings, debug, and skill initialization guides