Implement /team-onboarding on top of team and onboarding assets

[yaohaowei0914]

Background

The user-visible command list includes /team-onboarding, but the Bun reference does not expose a public implementation for it. Rust will need to treat this as a greenfield feature.

Reference

• No public command, skill, or plugin wrapper named /team-onboarding was found in the Bun tree.
• The closest available assets are generic onboarding, IDE onboarding, and team/swarm infrastructure.
• This means the Rust design should be grounded in existing local team/onboarding capabilities rather than a 1:1 port.

Rust Gap

• No /team-onboarding command today.
• Rust already has src/commands/team_cmd.rs and team foundations that can serve as the landing point.
• Suggested approach: define the real inputs first (usage history, team memory, project skills, common commands).

Acceptance

• /team-onboarding can generate a teammate-facing onboarding guide.
• The guide covers repo conventions, common commands, workflows, and risk areas.
• The output is grounded in real local/project/team state rather than being purely synthetic.
• Add tests and docs.