Overage: extra teams for $5/mo on Pro and $3/mo on Business #128

Part of #126.

Goal

A Pro or Business organization at its team limit can add teams for a monthly fee ($5 per team on Pro, $3 on Business), instead of upgrading. Free and Starter stay at one team and must upgrade.

Work

• Limit: the effective team limit is the plan limit plus the extra teams paid for. Keep this separate from the operator teams_limit_override used for grandfathering (0016_grandfather_team_limits), so a purchase never overwrites an operator decision.
• Billing: a recurring Dodo add-on priced per team, one price for Pro and one for Business. It follows the subscription: prorated when added, changed when the plan changes, and dropped when the subscription ends.
• Dashboard: when the team limit is reached, offer "Add a team for $X/mo" on the Teams tab and the Plan tab, and show extra teams in the Teams usage card.
• API, MCP, docs: document the purchase, include extra teams in the plan and usage responses, and update the pricing docs.

Acceptance criteria

• A Pro organization at 3 teams can buy a fourth with a Dodo test payment, then create the team.
• Changing plan Pro → Business keeps the extra teams and bills them at $3.
• Cancelling the subscription drops extra teams at period end, the same as other paid features.
• Tests cover the effective team limit with grandfathered overrides and bought teams together.