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/diary/edit_review.rs

@@ -34,6 +34,7 @@ pub async fn execute(deps: &EditReviewDeps, cmd: EditReviewCommand) -> Result<()
             .transpose()?,
         watched_at: cmd.watched_at,
         watch_medium: cmd.watch_medium,
+        spoilers: cmd.spoilers,
     });
 
     deps.review.update_review(&updated).await?;