docs: add WSL bridge troubleshooting

[lntutor]

Summary

• Add a WSL-specific troubleshooting section for the Windows Unreal Editor and WSL 2 bridge topology.
• Separate ZMQ connectivity checks from WSLg/OpenGL rendering checks.
• Document NAT versus mirrored networking, the required TCP ports, and EGL/GLFW/software-rendering fallbacks.

Motivation

WSL users can encounter two independent failure classes: the bridge cannot reach the Unreal process on Windows, or the dashboard cannot create its WSLg/MuJoCo rendering contexts. The new guide provides an ordered diagnosis so users can identify the failing layer before changing graphics or network settings.

Linked issue

Fixes #79

Build + test evidence

This is a documentation-only change; no plugin source, Unreal assets, native dependencies, or runtime behavior changed.

=== URLab documentation summary ===
Timestamp : 2026-07-19T12:23:41Z
Git HEAD  : b12b42d (docs/wsl-troubleshooting-79)
Docs      : Scripts/docs.sh build - passed (strict MkDocs build)
UE build  : Not run (documentation-only change)
UE tests  : Not run (documentation-only change)
===================================

Manual verification steps

1. Run Scripts/docs.sh build from the plugin root.
2. Open the generated Troubleshooting page.
3. Confirm the WSL section appears before the build-error entries and its Installation, Building from Source, and Sensors & Cameras links resolve.
4. Confirm the Bash and PowerShell commands render in their corresponding fenced code blocks.

Checklist

• Builds locally against UE 5.7+
• Full URLab.* automation suite passes
• Docs updated for user-facing changes

The Unreal build and automation checks were not run because this PR only changes Markdown documentation.