fix(analysis): emit Cancelled event + assert lock-release after cancel (0.87.13)

Two 0.87.4 follow-ups:

1. Cron tick: existing shutdown-on-cancel test now also asserts the
   advisory lock is re-acquirable after cancel-during-tick. Without
   this, a refactor moving `pg_advisory_unlock` under the cancel arm
   would ship green and break multi-replica safety.

2. Analysis worker: cancel-mid-dispatch left the dashboard banner stuck
   on the cancelled page until a later page overwrote it. Add a
   `Cancelled` AnalysisEvent variant, publish on the cancel-release
   branch, wire the analysis and admin overview dashboards to clear
   on it. Per-page chip rolls back from `analyzing` to `queued`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/tests/crawler_daemon.rs

@@ -894,4 +894,27 @@ async fn cron_shutdown_does_not_block_on_in_flight_metadata_pass(pool: PgPool) {
         started.elapsed() < Duration::from_secs(5),
         "shutdown took too long; cancel didn't propagate into the cron tick body"
     );
+
+    // The advisory lock must be released so another replica's cron can
+    // pick up the slot. Without this assertion, a refactor that moved
+    // the `pg_advisory_unlock` under the cancel arm (instead of running
+    // unconditionally below the select!) would ship green — only to
+    // wedge multi-replica deployments where the second replica's cron
+    // would block on `pg_try_advisory_lock` forever. `pg_try_advisory_lock`
+    // returns true iff the lock is free, so we use it as the probe.
+    let acquired: bool = sqlx::query_scalar("SELECT pg_try_advisory_lock($1)")
+        .bind(CRON_LOCK_KEY)
+        .fetch_one(&pool)
+        .await
+        .unwrap();
+    assert!(
+        acquired,
+        "advisory lock must be released after cancel-during-tick \
+         (otherwise multi-replica safety breaks)"
+    );
+    // Be a good citizen for whatever sqlx test runs next.
+    let _ = sqlx::query("SELECT pg_advisory_unlock($1)")
+        .bind(CRON_LOCK_KEY)
+        .execute(&pool)
+        .await;
 }