The finished_at field previously stored only a date, causing bag "finished"
timeline events to sort before same-day brews. Now stores a full datetime
and uses the actual close time for timeline ordering.
Replace ad-hoc to_domain/into_domain conversion methods on SQL
repository structs with idiomatic From and TryFrom trait implementations
on the record types, following standard Rust conventions.
Add domain update structs for brew and cup entities, add update()
methods to their repository traits and SQL implementations, and
expand UpdateBag with roast_id, roast_date, and amount fields.
