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/adapters/rss/src/lib.rs

@@ -22,9 +22,13 @@ impl RssFeedRenderer for RssAdapter {
                     e.movie().title().value(),
                     e.movie().release_year().value()
                 );
-                let description = match e.review().comment() {
-                    Some(c) => format!("{}/5 — {}", e.review().rating().value(), c.value()),
-                    None => format!("{}/5", e.review().rating().value()),
+                let description = match (e.review().comment(), e.review().spoilers()) {
+                    (Some(_), true) => format!(
+                        "{}/5 — contains spoilers",
+                        e.review().rating().value()
+                    ),
+                    (Some(c), false) => format!("{}/5 — {}", e.review().rating().value(), c.value()),
+                    (None, _) => format!("{}/5", e.review().rating().value()),
                 };
                 let pub_date = e
                     .review()