docs: add Local Network permission troubleshooting for Mac - #26279

Description

Adds a Mac troubleshooting topic for containers that can reach the internet but not devices on the local network (LAN). The cause is Docker Desktop not having the macOS Local Network permission: macOS then blocks container traffic to devices on the local network, including the router, while internet traffic still works. The fix is turning on Docker in System Settings > Privacy & Security > Local Network, which takes effect immediately, without restarting Docker Desktop.

Also adds a short Local Network permission section to the Mac permission requirements page that links to the new topic, since that page didn't mention it.

Verified on macOS 26.7 / Docker Desktop 4.92.0 by toggling Local Network for Docker:

• Off: containers couldn't reach LAN peers or the default gateway (ping, TCP, UDP DNS), while the internet and docker pull kept working.
• On: access came back immediately, on the same backend process, without restarting Docker Desktop.
• On a fresh install, macOS prompts for the Local Network permission, so users who hit this have most likely denied that prompt at some point.

Related issues or tickets

• [4.57.0 Regression] Containers cannot reach LAN hosts (worked in 4.56.0) desktop-feedback#636

Reviews

• Technical review @mat007
• Editorial review
• Product review