feat(v3): add Dozzle/Uptime Kuma/Gotify; fix Meilisearch catalogue re-index churn

- docker-compose: add dozzle, uptime-kuma, gotify services with Caddy subdomains
  (logs/uptime/push.libnovel.cc); bind-mount dozzle/users.yml for simple auth
- Caddyfile: add site blocks for logs, uptime, push subdomains
- admin layout: add Logs, Uptime, Push tabs to external tools pill
- CatalogueEntry: add Slug field; populated by novelfire scraper
- meili.Client: add BookExists() to check if a book is already indexed
- catalogue_refresh: skip books already present in Meilisearch to prevent
  redundant re-scraping and re-indexing on every runner restart
- docker-compose runner: set RUNNER_SKIP_INITIAL_CATALOGUE_REFRESH=true

v3/backend/internal/novelfire/scraper.go

@@ -111,7 +111,7 @@ func (s *Scraper) ScrapeCatalogue(ctx context.Context) (<-chan domain.CatalogueE
 				select {
 				case <-ctx.Done():
 					return
-				case entries <- domain.CatalogueEntry{Title: title, URL: bookURL}:
+				case entries <- domain.CatalogueEntry{Slug: slugFromURL(bookURL), Title: title, URL: bookURL}:
 				}
 			}