Docs: Add decision framework for when to add human members #313

Problem

The docs explain what human members are and how they work (pausing, routing, stale reminders), but they don't answer the key question new users ask:

When should I add someone as a human member vs. just @mention them on PRs?

This came up during onboarding — the distinction between a casual contributor and a roster-listed human isn't documented anywhere.

What's missing

Decision framework (the litmus test)

• Add to roster when the person is a decision gate — someone the team should actively route to, wait on, and track (e.g., Brady needs to approve architecture decisions before we build)
• Don't add when the person is a collaborator you interact with through normal GitHub flows — commenting on PRs, reviewing code, filing issues

Specific gaps across docs

Where this guidance should live

1. .squad/templates/human-members.md — the authoritative template (see companion issue for creating this file)
2. docs/src/content/docs/features/human-team-members.md — user-facing docs page
3. docs/src/content/docs/concepts/your-team.md — team composition overview

Proposed decision framework

Add a section like:

When to add a human member

The litmus test: If you want agents to stop and wait for someone's input before proceeding on a specific type of work, add them. If they review asynchronously via GitHub, don't bother.

Acceptance criteria

• Decision framework added to human-team-members.md docs page
• Brief mention added to your-team.md (link to full framework)
• Template file includes the framework (if created — see companion issue)