Plan 3: CLI + MCP server + CI + release pipeline

[ceballosiker]

Summary

Plan 3 of the exit-node build: produces v0.1's user-facing surface — the exitnode CLI, the exitnode-mcp stdio server, GitHub Actions CI, and goreleaser packaging.

• internal/core — Start(name), Stop(name), Destroy(name) + GetActive() accessor for the MCP layer
• cmd/exitnode — 8 cobra subcommands (up / down / rotate / list / status / health / pfsense sync / cost) over a shared buildCore helper; --json + --version + --verbose globals
• cmd/exitnode-mcp — stdio MCP server (modelcontextprotocol/go-sdk v1.6) with all 10 spec §11 tools wired to core
• examples/config.toml — annotated reference config
• examples/mcp.json — Claude Desktop / OpenClaw snippet
• .github/workflows/ci.yml — vet + lint + race tests + linux/darwin × amd64/arm64 cross-build matrix
• .goreleaser.yaml + release.yml — tag-triggered tar.gz archives + SHA256 + GitHub release
• README updated with Prerequisites, Install, Configure, Using exitnode-mcp, and Troubleshooting sections
• go.mod cleaned via go mod tidy (long-deferred since Plan 1; safe now that both binaries import everything)

Test plan

• make test (race, all 9 packages green)
• make test-integration (build-tagged path compiles)
• go vet ./... and go vet -tags integration ./... clean
• 4-platform × 2-binary cross-compile smoke
• exitnode --help shows all 8 subcommands; exitnode --version returns the ldflag-injected string
• manual integration smoke against real GCP (post-merge)

Next: cut develop → main and a v0.1.0 tag to fire the goreleaser release workflow.