fix(security): critical — repair PIN reset + enforce real prod secrets

C1: reset_user_pin wrote to a non-existent column (pin_failed_attempts);
    the real column is failed_pin_attempts, so every PIN reset 500'd. Fixed
    the column name; new e2e (pin-reset.spec.ts) proves a reset returns a
    usable PIN and the target can recover with it.

C2: config.rs::validate_secrets now rejects placeholder-ish secrets
    (change_me/dev_secret/placeholder), enforces len>=32 in prod, and
    requires a real ADMIN_PASSWORD_HASH. docker-compose.yml sets
    APP_ENV=production so the guard actually runs. Corrected the false
    "fixed" claim in SECURITY-BACKLOG.md. .env.example documents the rule.

Riders in these files (documented here since git can't split hunks):
- host.rs also carries the event-scoped ban_user fix and the
  close_event/open_event no-op broadcast guard (medium).
- docker-compose.yml also adds ORIGIN (H6), app/frontend healthchecks with
  Caddy waiting on health, and per-service memory limits (medium).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/handlers/host.rs

@@ -113,10 +113,11 @@ pub async fn ban_user(
     }
 
     sqlx::query(
-        "UPDATE \"user\" SET is_banned = TRUE, uploads_hidden = $2 WHERE id = $1",
+        "UPDATE \"user\" SET is_banned = TRUE, uploads_hidden = $2 WHERE id = $1 AND event_id = $3",
     )
     .bind(user_id)
     .bind(body.hide_uploads)
+    .bind(auth.event_id)
     .execute(&state.pool)
     .await?;
 
@@ -263,7 +264,7 @@ pub async fn reset_user_pin(
     sqlx::query(
         "UPDATE \"user\"
          SET recovery_pin_hash = $1,
-             pin_failed_attempts = 0,
+             failed_pin_attempts = 0,
              pin_locked_until = NULL
          WHERE id = $2",
     )
@@ -341,14 +342,18 @@ pub async fn close_event(
     State(state): State<AppState>,
     RequireHost(_auth): RequireHost,
 ) -> Result<StatusCode, AppError> {
-    sqlx::query(
+    let result = sqlx::query(
         "UPDATE event SET uploads_locked_at = NOW() WHERE slug = $1 AND uploads_locked_at IS NULL",
     )
     .bind(&state.config.event_slug)
     .execute(&state.pool)
     .await?;
 
-    let _ = state.sse_tx.send(SseEvent::new("event-closed", "{}"));
+    // Only broadcast when this call actually flipped the lock — closing an
+    // already-closed event is a no-op and shouldn't spam listeners.
+    if result.rows_affected() > 0 {
+        let _ = state.sse_tx.send(SseEvent::new("event-closed", "{}"));
+    }
 
     Ok(StatusCode::NO_CONTENT)
 }
@@ -357,14 +362,16 @@ pub async fn open_event(
     State(state): State<AppState>,
     RequireHost(_auth): RequireHost,
 ) -> Result<StatusCode, AppError> {
-    sqlx::query(
-        "UPDATE event SET uploads_locked_at = NULL WHERE slug = $1",
+    let result = sqlx::query(
+        "UPDATE event SET uploads_locked_at = NULL WHERE slug = $1 AND uploads_locked_at IS NOT NULL",
     )
     .bind(&state.config.event_slug)
     .execute(&state.pool)
     .await?;
 
-    let _ = state.sse_tx.send(SseEvent::new("event-opened", "{}"));
+    if result.rows_affected() > 0 {
+        let _ = state.sse_tx.send(SseEvent::new("event-opened", "{}"));
+    }
 
     Ok(StatusCode::NO_CONTENT)
 }