Document Linux installer and agent updates

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Summary

• Updated Linux installation docs with installer-script usage, key INSTALL_JUICE_* variables, service argument passing, pool-name quoting, and default service data/log paths.
• Updated system requirements with the Linux installer glibc check and agent dependency expectations, including libnvidia-encode.
• Updated Docker agent docs for the current Ubuntu 24.04/CUDA 13 image build path, required local build inputs, build args, and corrected docker run example.
• Updated troubleshooting/log docs with Docker UDP/JUICE_HOST_IP guidance and Linux installer service log collection.

Codepaths Covered

• installer/install-juice.sh: installer env vars, optional INSTALL_JUICE_POOL, quoted pool values, service command construction, dependency checks, and service log path.
• docker/agent/Dockerfile: Ubuntu 24.04 base, CUDA 13 runtime libraries, required build artifacts, and image layout.
• docker/agent/root/home/juice/start-agent.sh: required container env vars and gateway host/port behavior.
• docker/agent/README.md: Docker env vars, build inputs, and run examples.

Note: Juice-Labs/juice was not resolvable from this cloud environment via gh; these updates were verified against the accessible Juice-Labs/juice-oss source and recent merged PRs there.

Key Knowledge Gaps Addressed

• When the Linux installer installs only CLI binaries versus a persistent agent service.
• How to pass service flags and quote pool names that contain spaces.
• Which libraries block Linux client installs versus agent service installs.
• What files are needed to build a custom Docker agent image and how to expose the agent UDP port.
• Where to collect logs for Linux services installed by the installer.

Validation

• git diff --check origin/master...HEAD
• npm run build succeeds. Docusaurus reports existing broken /juice-docs/edit?path=... links and stale Browserslist data, but the build completes successfully.