skill development workflow improvements

### Problem Statement

1. Skill development and dependency management are tightly constrained by the current sandbox: the filesystem is mostly read‑only, outbound network access is allow‑listed, and build tools are removed. As a result, users usually have to edit Dockerfiles and rebuild images for any new dependency, which slows down prototyping and makes skill evolution harder.

### Proposed Design

1. Provide a more flexible, officially supported development path for skills
2. Maybe find a much better trade-off between security and maintainability here.

### Alternatives Considered

_No response_

### Category

enhancement: feature

### Checklist

- [x] I searched existing issues and this is not a duplicate
- [x] This is a design proposal, not a "please build this" request