fix(security): cross-event authz, SSE ticket flow, account hardening, audit logs

Follow-up to the comprehensive code review. Five batches:

1. Cross-event authorization: host_delete_upload, unban_user, and
   host_delete_comment now scope by auth.event_id. Adds
   Upload::find_by_id_and_event / soft_delete_in_event and a
   Comment::soft_delete_in_event variant that joins through upload.

2. Token exposure: SSE auth no longer puts the JWT in the URL.
   New /api/v1/stream/ticket endpoint mints a short-lived single-use
   ticket bound to the session; the EventSource passes ?ticket=...
   instead. Refuse to start in APP_ENV=production with the dev JWT
   sentinel; warn loudly otherwise.

3. Account hardening: per-IP+name rate limit on /recover (mitigates
   targeted lockout DoS), per-IP rate limit on /admin/login, random
   32-char admin recovery PIN (replaces "0000"), structured tracing
   events for wrong PIN, lockout, failed admin login, ban/unban/role
   change/pin-reset/host-delete.

4. DoS / correctness: comment listing paginated (LIMIT 50 + ?before=
   cursor), hashtag extraction whitelisted to ASCII alnum+underscore
   (≤40 chars) with unit tests, display_name / caption / comment body
   length validated in chars rather than bytes.

5. Cleanup: session-touch failures now logged, DATABASE_MAX_CONNECTIONS
   env var (default 10).

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

backend/src/handlers/host.rs

@@ -120,18 +120,38 @@ pub async fn ban_user(
     .execute(&state.pool)
     .await?;
 
+    tracing::info!(
+        actor_user_id = %auth.user_id,
+        target_user_id = %user_id,
+        event_id = %auth.event_id,
+        hide_uploads = body.hide_uploads,
+        "host: ban_user"
+    );
+
     Ok(StatusCode::NO_CONTENT)
 }
 
 pub async fn unban_user(
     State(state): State<AppState>,
-    RequireHost(_auth): RequireHost,
+    RequireHost(auth): RequireHost,
     Path(user_id): Path<Uuid>,
 ) -> Result<StatusCode, AppError> {
-    sqlx::query("UPDATE \"user\" SET is_banned = FALSE WHERE id = $1")
-        .bind(user_id)
-        .execute(&state.pool)
-        .await?;
+    let result = sqlx::query(
+        "UPDATE \"user\" SET is_banned = FALSE WHERE id = $1 AND event_id = $2",
+    )
+    .bind(user_id)
+    .bind(auth.event_id)
+    .execute(&state.pool)
+    .await?;
+    if result.rows_affected() == 0 {
+        return Err(AppError::NotFound("Benutzer nicht gefunden.".into()));
+    }
+    tracing::info!(
+        actor_user_id = %auth.user_id,
+        target_user_id = %user_id,
+        event_id = %auth.event_id,
+        "host: unban_user"
+    );
     Ok(StatusCode::NO_CONTENT)
 }
 
@@ -181,6 +201,14 @@ pub async fn set_role(
         .bind(auth.event_id)
         .execute(&state.pool)
         .await?;
+    tracing::info!(
+        actor_user_id = %auth.user_id,
+        target_user_id = %user_id,
+        event_id = %auth.event_id,
+        old_role = %target.0,
+        new_role,
+        "host: set_role"
+    );
     Ok(StatusCode::NO_CONTENT)
 }
 
@@ -251,38 +279,61 @@ pub async fn reset_user_pin(
         serde_json::json!({ "user_id": user_id }).to_string(),
     ));
 
+    tracing::info!(
+        actor_user_id = %auth.user_id,
+        target_user_id = %user_id,
+        event_id = %auth.event_id,
+        "host: reset_user_pin"
+    );
+
     Ok(Json(PinResetResponse { pin }))
 }
 
 pub async fn host_delete_upload(
     State(state): State<AppState>,
-    RequireHost(_auth): RequireHost,
+    RequireHost(auth): RequireHost,
     Path(upload_id): Path<Uuid>,
 ) -> Result<StatusCode, AppError> {
-    let upload = Upload::find_by_id(&state.pool, upload_id)
+    let upload = Upload::find_by_id_and_event(&state.pool, upload_id, auth.event_id)
         .await?
         .ok_or_else(|| AppError::NotFound("Upload nicht gefunden.".into()))?;
 
-    Upload::soft_delete(&state.pool, upload_id).await?;
+    let deleted = Upload::soft_delete_in_event(&state.pool, upload_id, auth.event_id).await?;
+    if !deleted {
+        return Err(AppError::NotFound("Upload nicht gefunden.".into()));
+    }
 
     let _ = state.sse_tx.send(SseEvent::new(
         "upload-deleted",
         serde_json::json!({ "upload_id": upload.id }).to_string(),
     ));
 
+    tracing::info!(
+        actor_user_id = %auth.user_id,
+        event_id = %auth.event_id,
+        upload_id = %upload.id,
+        "host: host_delete_upload"
+    );
+
     Ok(StatusCode::NO_CONTENT)
 }
 
 pub async fn host_delete_comment(
     State(state): State<AppState>,
-    RequireHost(_auth): RequireHost,
+    RequireHost(auth): RequireHost,
     Path(comment_id): Path<Uuid>,
 ) -> Result<StatusCode, AppError> {
-    Comment::find_by_id(&state.pool, comment_id)
-        .await?
-        .ok_or_else(|| AppError::NotFound("Kommentar nicht gefunden.".into()))?;
-
-    Comment::soft_delete(&state.pool, comment_id).await?;
+    let deleted =
+        Comment::soft_delete_in_event(&state.pool, comment_id, auth.event_id).await?;
+    if !deleted {
+        return Err(AppError::NotFound("Kommentar nicht gefunden.".into()));
+    }
+    tracing::info!(
+        actor_user_id = %auth.user_id,
+        event_id = %auth.event_id,
+        comment_id = %comment_id,
+        "host: host_delete_comment"
+    );
     Ok(StatusCode::NO_CONTENT)
 }