feat: agent-first CLI for alpha launch

[ashishmax31]

Summary

• add agent-friendly authentication, scope discovery, stack context selection, structured output, actionable errors, and no-argument help
• add authenticated stackdome api, doctor, stackfile import/export, Postgres shortcuts and waits, and improved build/log/release workflows
• make deploy and rollback waits verify the requested release, terminal state, convergence, runtime health, and public URLs only for exposed ports
• distinguish latest rollout from the serving release in status output and support stack references by name, full ID, or unique prefix
• sync the CLI stackfile implementation with the updated Hub package and add cross-platform release automation for macOS, Linux, and Windows

Agent-facing behavior

• JSON/YAML output is available for automation-oriented command paths
• streaming JSON uses NDJSON where appropriate
• stackdome api <path> reuses CLI authentication and scope
• errors include the next command to resolve missing context
• secrets and tokens are redacted from diagnostic output

Verification

• go test ./... -count=1
• go vet ./...
• GOOS=windows GOARCH=amd64 go build ./...
• git diff --check
• final combined code review: no Critical or Important findings

Overlap with #3

PR #3 remains open and overlaps in distribution/auth plumbing, especially .github/workflows/release.yml and URL/auth normalization. Its installer and GoReleaser files are not included here. This PR contains the broader agent-first CLI launch work and its integrated test coverage.