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/template-askama/templates/profile.html

@@ -219,9 +219,17 @@
             <span class="star {% if filled %}filled{% else %}empty{% endif %}">★</span>
           {% endfor %}
         </div>
+        {% let author = ctx.is_current_user(entry.review().user_id().value()) %}
         {% if let Some(comment) = entry.review().comment() %}
+        {% if !author && entry.review().spoilers() %}
+        <details class="comment spoiler">
+          <summary style="cursor:pointer;opacity:.75">Contains spoilers</summary>
+          {{ comment.value() }}
+        </details>
+        {% else %}
         <div class="comment">{{ comment.value() }}</div>
         {% endif %}
+        {% endif %}
         <div class="watched-at">{{ entry.review().watched_at().format("%Y-%m-%d") }}</div>
         {% if ctx.is_current_user(entry.review().user_id().value()) %}
         <form method="post" action="/reviews/{{ entry.review().id().value() }}/delete" class="delete-form">