Ensures author avatar is only displayed if it exists.
Uses dynamic league IDs from the `spielbetrieb` page in the navbar, which
allows changing the league links in the backend.
Removed outdated articles (`20250709-Test`, `test` in drafts) and introduced two new posts: `vereinsblitzmeisterschaft` and `kreismannschaftspokal`. Added associated images and improved structured content with blocks, summaries, and tags for better organization.
tfeigel