IDE companion extension fails to connect with gVisor (runsc) sandbox

## Problem

The VSCode IDE companion extension fails to connect when using `GEMINI_SANDBOX=runsc` (gVisor), while it works correctly with `GEMINI_SANDBOX=docker`. This prevents all IDE integration features (`/ide status`, `/ide enable`, IDE-aware tools) from functioning when using gVisor sandboxing.

## Root Cause

The IDE companion uses **HTTP over TCP** to communicate between the container and the host VSCode instance.

## Additional Context

- gVisor is designed for stronger isolation, so this limitation is somewhat expected
- The issue affects all IDE integration features, not just connection status
- STDIO-based connection would be the most elegant solution as it works regardless of isolation level
- This should be documented in sandbox capability matrix