Teach remote-training skill local desktop/notebook serving

[vertix]

Summary

PR #392 rewrote the remote-training skill for Nebius Serverless and dropped the local Docker-context serving path entirely — but that path is still valid (the desktop/notebook contexts and docker/docker-compose.yml services remain in the repo) and is the right tool for consumer-GPU inference (LeRobot/ACT/SmolVLA, GR00T inference) without paying for H100.

• Add a "Serving locally (desktop / notebook)" section: canonical docker --context <ctx> compose run --service-ports <server> pattern, the CACHE_ROOT=/home/vertix quirk, preset/serve subcommand, detached running, client wiring, and the GR00T-OOM / port-conflict gotchas. Defers to docker/CONTEXTS.md + docker-compose.yml as source of truth.
• Broaden the skill's frontmatter trigger description so it activates for local-serving requests, not just Nebius ones.
• Does not revert the Nebius rewrite or restore the obsolete VM/SSH (vm-train) machinery — that part is genuinely superseded by Serverless.

Test plan

• Docs-only change to a .claude/ skill; no code paths affected.
• Command patterns and service names were sourced from the content removed in Serverless endpoint auto-shutdown + remote-training skill for Nebius Serverless #392 and the still-current docker/CONTEXTS.md / docker-compose.yml. Not executed (requires the desktop/notebook Docker contexts).