Reusable Subscription Domain and PostgreSQL Model

Define a host-integration boundary for billable owners, authorized actors, and eligible seat assignees using stable owner-type and owner-ID references that support individuals and teams.

Implement versioned TypeORM plan and price entities for fixed recurring fees, per-seat fees, billing intervals, currencies, feature entitlements, and retired offerings, storing monetary amounts in minor units.

Define and test an explicit subscription state machine with allowed command-driven and provider-event-driven transitions and invariants.

Implement PostgreSQL migrations for subscriptions, billing periods, provider references, and transition audit records, including appropriate unique, foreign-key, and check constraints.