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/meili/client.go

@@ -29,6 +29,9 @@ const indexName = "books"
 type Client interface {
 	// UpsertBook adds or updates a book document in the search index.
 	UpsertBook(ctx context.Context, book domain.BookMeta) error
+	// BookExists reports whether a book with the given slug is already in the
+	// index. Used by the catalogue refresh to skip re-indexing known books.
+	BookExists(ctx context.Context, slug string) bool
 	// Search returns up to limit books matching query.
 	Search(ctx context.Context, query string, limit int) ([]domain.BookMeta, error)
 	// Catalogue queries books with optional filters, sort, and pagination.
@@ -172,6 +175,15 @@ func (c *MeiliClient) UpsertBook(_ context.Context, book domain.BookMeta) error
 	return nil
 }
 
+// BookExists reports whether the slug is already present in the index.
+// It fetches the document by primary key; a 404 or any error is treated as
+// "not present" (safe default: re-index rather than silently skip).
+func (c *MeiliClient) BookExists(_ context.Context, slug string) bool {
+	var doc bookDoc
+	err := c.idx.GetDocument(slug, nil, &doc)
+	return err == nil && doc.Slug != ""
+}
+
 // Search returns books matching query, up to limit results.
 func (c *MeiliClient) Search(_ context.Context, query string, limit int) ([]domain.BookMeta, error) {
 	if limit <= 0 {
@@ -306,6 +318,7 @@ func sortStrings(s []string) {
 type NoopClient struct{}
 
 func (NoopClient) UpsertBook(_ context.Context, _ domain.BookMeta) error { return nil }
+func (NoopClient) BookExists(_ context.Context, _ string) bool           { return false }
 func (NoopClient) Search(_ context.Context, _ string, _ int) ([]domain.BookMeta, error) {
 	return nil, nil
 }