[DOCS] Update `/sandbox` command documentation to reflect macOS/Linux exclusivity

Documentation Type

Missing documentation (feature not documented)

Documentation Location

• https://code.claude.com/docs/en/slash-commands

Section/Topic

• The "Built-in slash commands" table.

Current Documentation

The table currently lists the command as:
| /sandbox | Enable sandboxed bash tool with filesystem and network isolation for safer, more autonomous execution |

What's Wrong or Missing?

While the dedicated feature page at https://code.claude.com/docs/en/sandboxing correctly notes that "Windows support [is] planned," the main Slash Commands reference page lists it as a standard built-in command without any platform caveats.

This is confusing for native Windows users who see the command in the documentation but are unable to use the feature. Similar platform-specific constraints (like those for /terminal-setup) are often noted in documentation to manage user expectations.

Suggested Improvement

Update the description in the Slash Commands table to explicitly mention the platform restriction.

Suggested Text:
| /sandbox | Enable sandboxed bash tool (macOS and Linux only) with filesystem and network isolation for safer, more autonomous execution |

Impact

High - Prevents users from using a feature

Additional Context

• The platform support is explicitly restricted in the detailed guide here: https://code.claude.com/docs/en/sandboxing#platform-support
• The settings.json reference also notes this restriction for the sandbox object: https://code.claude.com/docs/en/settings#sandbox-settings
• Adding this note to the primary command table ensures users don't have to click through to a sub-page to realize a command is unavailable for their OS.