Feat/remote coding profile root help (#31)

* feat: builtin remote-coding profile and root help for sync/agent

Ship a durable remote lab profile (persistent, 4c/8G/32G, grain-ubuntu)
without config, list it from grain profile ls, and surface sync + agent
deploy in grain --help for discoverability before the next release.

* chore: commit mise.toml for pinned Go, golangci-lint, pre-commit

just init already calls mise install, but the repo only had .tool-versions.
Add mise.toml so mise users get the same pins without guessing.

Author: cxdy