fix(examples): pin HOME so plugin caches resolve under appuser

[u9g]

Summary

• Docker's USER directive switches UID/GID but doesn't set $HOME from /etc/passwd, so plugin asset caches under $HOME/.cache (Silero VAD, the LiveKit turn detector, HuggingFace, etc.) land in /root instead of /app and the worker can't find them at startup.
• Pinning ENV HOME="/app" makes the cache path deterministic for appuser.
• This is the upstream version of a fix carried in the agent-starter-node template (livekit-examples/agent-starter-node#46).

Test plan

• Build the example image and confirm download-files writes under /app/.cache/....
• Deploy to LiveKit Cloud and confirm the worker boots without re-downloading plugin assets.

🤖 Generated with Claude Code

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[devin-ai-integration]

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