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/application/src/integrations/confirm.rs

@@ -53,6 +53,7 @@ pub async fn execute(
             comment: c.comment,
             watched_at: *event.watched_at(),
             watch_medium: Some(domain::value_objects::WatchMedium::MediaServer),
+            spoilers: false,
         };
 
         deps.review_logger.log_review(review_cmd).await?;