Update Fiction Book Writing preset to v1.8.1 (#2714)

Update fiction-book-writing preset submitted by @adaumann to:
- presets/catalog.community.json (version, download_url, provides, updated_at)
- docs/community/presets.md community presets table

Changes from v1.7.0:
- 25 templates (was 22), 33 commands (was 27), 2 scripts
- RAG search stability update

Closes #2691