docs: sync command specification

[steipete]

Summary

• remove retired schedule CRUD and metrics summary/aggregate commands from the specification
• document current away, audio favorites, travel plan, logout, base test, and Autopilot command names
• align README command names with Cobra's current command tree

Proof

• compared README and docs/spec.md against current Cobra help and command registration
• go test ./...
• git diff --check
• autoreview skipped: documentation-only command inventory correction with source/help verification

Risk

Low. Documentation only; no runtime behavior changes.

[steipete]

Landed as e20df05.

Proof on PR head 5fae0ed850e2a7f01648704bda60b20d0d085ee3:

• compared README and docs/spec.md against current Cobra help and command registration
• go test ./...
• git diff --check
• exact-head CI: https://github.com/steipete/eightctl/actions/runs/28507682766 passed; GitGuardian passed
• autoreview skipped because this was a documentation-only command inventory correction with direct source/help verification

No external Eight Sleep API proof applies to documentation-only corrections.