Update Contract Lifecycle Settings

The company's renewal reminder policy, as the settings page sends it.

Every field is required: this is the whole policy, not a patch, so a save from a stale page cannot half-apply. The two default_* columns on the table are absent on purpose — nothing reads them yet (see upsert_contract_lifecycle_settings), and a request field nothing acts on is a promise the product does not keep.

Two cadences and two recipient roles, on independent axes. The cadences belong to the term's two dates — a notice deadline wants months of warning, a renewal date wants days — and each date carries a switch that turns its ladder off for the whole company. The roles are the two groups of people reminded on both, for the life of the term (unioned at send time, not stored — see resolve_term_assignees): the assignees own the renewal decision, the subscribers are kept in the loop.

The switches are separate fields rather than an empty cadence: the ladder is bounded at one lead day minimum, so an empty list would be a second way to say "off" that the CHECK rejects — and a company turning a date back on would have lost the schedule it had.

Each role is a set, so a company can name two teams and a person for one of them. An empty role is a role nobody fills: it resolves to nobody rather than falling back, which is why the settings page blocks the save. Which id belongs with which mode — and whether the mode is in a contract's scope — is checked by the endpoint against the company's directory, since that needs a database.

The company's resolved lifecycle settings.

Always concrete values: an unconfigured company gets the code defaults with is_configured=False, so the UI can render "using defaults" without null-branching every field.