Return structured, read-only system and runtime information for the current machine/workspace.

Use `sysinfo` when the user asks for:
- system information
- OS / runtime / shell summary
- CPU / memory / disk summary
- current workspace / package-manager / git-repo context

Prefer `sysinfo` over raw `bash` when the goal is a concise environment summary.

Parameters:
- `sections` (optional): array of section names to return. Supported:
  - `os`
  - `runtime`
  - `workspace`
  - `cpu`
  - `memory`
  - `disk`
- `path` (optional): workspace path to inspect for `workspace` / `disk` sections

Examples:
- `sysinfo()`
- `sysinfo(sections=["os","runtime","workspace"])`
- `sysinfo(sections=["disk"], path=".")`

Safety:
- This tool is read-only.
- It does not dump full environment variables or process lists.
- Use `bash` only when the user truly needs deeper platform-specific diagnostics.
