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/tests/forms.rs

@@ -10,6 +10,7 @@ fn make_form(watched_at: &str) -> LogReviewForm {
         comment: None,
         watched_at: watched_at.to_string(),
         watch_medium: None,
+        spoilers: false,
         csrf_token: String::new(),
     }
 }
@@ -24,6 +25,7 @@ fn make_request(watched_at: &str) -> LogReviewRequest {
         comment: None,
         watched_at: watched_at.to_string(),
         watch_medium: None,
+        spoilers: false,
     }
 }