Split domain/models/mod.rs (630 lines) into focused files:
movie.rs, review.rs, user.rs, stats.rs, enrichment.rs, feed.rs.
Move URL/date formatting from application use cases to
presentation mappers — use cases now return raw domain data.
Delete watchlist/get_page.rs (was pure presentation logic),
replace with presentation/mappers/watchlist.rs.
Document signature conventions in CONTRIBUTING.md.
