Announced pages: event windows, header announcements, summary tasks

A question may carry event: {starts, duration, place}. While the
window is open the page is announced in a strip at the top of every
header (name, when, 'in 3 days'), soonest first, and kept out of the
footer nav; when it closes the page becomes a followup - only a
visitor carrying an answer chain still sees it.

announce.rs keeps one record per event page in the runtime-owned
portal_events bucket (built-in state graph: announced ->
awaiting_summary -> summarized, content may override) and, on a
one-minute idempotent sweep, moves ended windows to awaiting_summary,
publishing the transition on portal.answers.submitted as 'Summary
due' - the post-what-happened task a review desk picks up. Lint
warns when event pages exist but nothing reads portal_events.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/main.rs

@@ -30,7 +30,9 @@ async fn main() -> anyhow::Result<()> {
     let content_branch = std::env::var("CONTENT_BRANCH").unwrap_or_else(|_| "main".to_string());
     let gitea_base = content::gitea_api_base(&content_repo)?;
     let content_raw_base = content::gitea_raw_base(&content_repo)?;
-    let aggregates = content::load_aggregates_from_gitea(&content_repo, &content_branch).await?;
+    let aggregates = content::with_builtin_aggregates(
+        content::load_aggregates_from_gitea(&content_repo, &content_branch).await?,
+    );
     let questions = content::load_questions_from_gitea(&content_repo, &content_branch, "questions").await?;
     content::validate_questions(&questions, &aggregates)?;
     let site = content::load_site_from_gitea(&content_repo, &content_branch).await?;
@@ -89,6 +91,10 @@ async fn main() -> anyhow::Result<()> {
         garage,
     };
 
+    // Announced pages: keep their desk records current, close ended
+    // windows (see announce.rs).
+    tokio::spawn(portal::announce::run(state.clone()));
+
     // Dev-friendly defaults: in-memory sessions, secure cookies only when
     // COOKIE_SECURE=true (set it behind TLS in production) - same
     // defaults cnats uses. SameSite=Lax (tower-sessions defaults to