feat(cli): standardize command examples and next-step remediation hints across the CLI

[kjw3]

Problem

Some commands, like deploy, provide examples and recovery hints well. Others do not. The result is inconsistent UX across the CLI.

Scope

• Add examples to command help and common error paths
• Standardize "what to run next" guidance for missing setup, missing sandbox, missing credentials, and invalid subcommands

Acceptance Criteria

• Every user-facing command has at least one example in help text
• Common failures suggest the next command to run
• Unknown action errors for sandbox commands list valid actions and a concrete example

Context

This came out of a CLI review against https://clig.dev/. It is a follow-on usability improvement after per-command help.

[wscurran]

✨ Possibly related open PRs:

• #826 feat: add CLI metrics collection and stats command
• #644 feat(cli): add self-update command
• #274 feat(cli): add setup-apple command for macOS/Apple Silicon