test(cli): add Copilot CLI subprocess integration tests for SQUAD_TEAM_ROOT #836

Follow-up from PR #763 (Amanda Silver)

PR #763 fixed subprocess resolution for nap/status/cost, but there are no end-to-end tests verifying Squad works correctly when invoked by Copilot CLI.

Action Items

1. Document the Copilot CLI bang command workflow — how !squad nap invokes Squad as a subprocess
2. Add E2E test or manual test script that simulates subprocess invocation with a different cwd
3. Verify --team-root flag propagation — when Squad dispatches child processes (e.g., watch → dispatch), does SQUAD_TEAM_ROOT propagate correctly?

Why This Matters

• Squad is increasingly used inside Copilot CLI
• Bang commands on Windows set cwd to system directories
• Watch dispatch spawns child processes that also need correct resolution

Related

• PR fix(cli): wire SQUAD_TEAM_ROOT into squad resolution for subprocess compatibility (#734) #763 — initial subprocess fix
• Issue bug: squad nap fails when invoked via bang command (!) in Windows PowerShell terminal #734 — original bug report