v0.13.0 — isolated team board

A spawned team's board is now isolated by default (its own scoped beads DB, not the repo's committed .beads) — so a team on a repo with an existing board never resumes/pollutes it, only works what the PM dispatches. shared_board=True opts back into the repo's board. No projectBoard-plugin change (it already honors db_path). 90 tests.