Add Spoiler Flag with veil, AP content-warning encoding, and full-stack plumbing

Authors can flag a review's comment as containing spoilers; the comment is
blurred behind a reveal control for every viewer except the author, omitted
from RSS, and federates as containsSpoilers plus an AP summary content
warning (ADR-0011) so Mastodon-class clients also collapse it. Flag follows
the general-edit path (ADR-0001) across domain, both DB backends, REST,
HTML templates, SPA (shadcn), TUI fixtures, and exports.

crates/presentation/src/mappers/movies.rs

@@ -38,6 +38,7 @@ pub fn review_to_dto(review: &Review) -> ReviewDto {
         comment: review.comment().map(|c| c.value().to_string()),
         watched_at: domain::value_objects::format_watched_at(review.watched_at()),
         watch_medium: review.watch_medium().copied(),
+        spoilers: review.spoilers(),
     }
 }