Document agent installer and Docker setup details

[cursor]

Summary

• Updated the Linux GPU sharing guide with the installer-based agent service flow, required INSTALL_JUICE_TOKEN/INSTALL_JUICE_POOL variables, quoted pool-name examples, pass-through agent arguments, and dependency checks.
• Expanded the Docker agent guide with runtime environment variables, --gpus all examples, host port/IP troubleshooting, and custom build artifact requirements.

Codepaths covered

• juice-oss/installer/install-juice.sh: service installation only when INSTALL_JUICE_POOL is set, support for quoted pool names, pass-through agent run arguments, systemd/OpenRC and library checks.
• juice-oss/docker/agent/Dockerfile and docker/agent/root/home/juice/start-agent.sh: required build inputs, Linux/NVIDIA runtime expectations, JUICE_* environment variables, GPU exposure, and UDP host port mapping.

Knowledge gaps addressed

• How to install a Linux agent service directly from the installer rather than only from an existing CLI.
• How to handle pool names with spaces during installer-based setup.
• What files must be present to build a custom Docker agent image.
• What Docker environment variables and network/GPU checks matter when clients cannot connect.

Verification

• npm run build passed after npm ci installed dependencies.
• Build still reports existing site-wide broken edit-link warnings unrelated to this docs change.