chore: migrate to v3, Doppler secrets, clean up legacy code

- Remove all pre-v3 code: scraper, ui-v2, backend v1, ios v1+v2, legacy CI workflows
- Flatten v3/ contents to repo root
- Add Doppler secrets management (project=libnovel, config=prd)
- Add justfile with doppler run wrappers for all docker compose commands
- Strip hardcoded env fallbacks from docker-compose.yml
- Add minimal README.md
- Clean up .gitignore

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}:
 				}
 			}
 
@@ -194,8 +194,12 @@ func (s *Scraper) ScrapeMetadata(ctx context.Context, bookURL string) (domain.Bo
 
 // ── ChapterListProvider ───────────────────────────────────────────────────────
 
-// ScrapeChapterList returns all chapter references for a book, ordered ascending.
-func (s *Scraper) ScrapeChapterList(ctx context.Context, bookURL string) ([]domain.ChapterRef, error) {
+// ScrapeChapterList returns chapter references for a book, ordered ascending.
+// upTo > 0 stops pagination as soon as at least upTo chapter numbers have been
+// collected — use this for range scrapes so we don't paginate 100 pages just
+// to discover refs we'll never scrape. upTo == 0 fetches all pages.
+// Each page fetch uses retryGet with 429-aware exponential backoff.
+func (s *Scraper) ScrapeChapterList(ctx context.Context, bookURL string, upTo int) ([]domain.ChapterRef, error) {
 	var refs []domain.ChapterRef
 	baseChapterURL := strings.TrimRight(bookURL, "/") + "/chapters"
 	page := 1
@@ -210,7 +214,7 @@ func (s *Scraper) ScrapeChapterList(ctx context.Context, bookURL string) ([]doma
 		pageURL := fmt.Sprintf("%s?page=%d", baseChapterURL, page)
 		s.log.Info("scraping chapter list", "page", page, "url", pageURL)
 
-		raw, err := s.client.GetContent(ctx, pageURL)
+		raw, err := retryGet(ctx, s.log, s.client, pageURL, 9, 6*time.Second)
 		if err != nil {
 			return refs, fmt.Errorf("chapter list page %d: %w", page, err)
 		}
@@ -255,6 +259,13 @@ func (s *Scraper) ScrapeChapterList(ctx context.Context, bookURL string) ([]doma
 			})
 		}
 
+		// Early-stop: if we have seen at least upTo chapter numbers, we have
+		// enough refs to cover the requested range — no need to paginate further.
+		if upTo > 0 && len(refs) > 0 && refs[len(refs)-1].Number >= upTo {
+			s.log.Debug("chapter list early-stop reached", "upTo", upTo, "collected", len(refs))
+			break
+		}
+
 		page++
 	}