fix: add DeduplicateChapters stub to test mocks to satisfy BookWriter interface

backend/internal/bookstore/bookstore_test.go

@@ -39,8 +39,9 @@ func (m *mockStore) ReadChapter(_ context.Context, _ string, _ int) (string, err
 func (m *mockStore) ListChapters(_ context.Context, _ string) ([]domain.ChapterInfo, error) {
 	return nil, nil
 }
-func (m *mockStore) CountChapters(_ context.Context, _ string) int            { return 0 }
-func (m *mockStore) ReindexChapters(_ context.Context, _ string) (int, error) { return 0, nil }
+func (m *mockStore) CountChapters(_ context.Context, _ string) int                { return 0 }
+func (m *mockStore) ReindexChapters(_ context.Context, _ string) (int, error)     { return 0, nil }
+func (m *mockStore) DeduplicateChapters(_ context.Context, _ string) (int, error) { return 0, nil }
 
 // RankingStore
 func (m *mockStore) WriteRankingItem(_ context.Context, _ domain.RankingItem) error { return nil }
@@ -52,10 +53,10 @@ func (m *mockStore) RankingFreshEnough(_ context.Context, _ time.Duration) (bool
 }
 
 // AudioStore
-func (m *mockStore) AudioObjectKey(_ string, _ int, _ string) string          { return "" }
-func (m *mockStore) AudioObjectKeyExt(_ string, _ int, _, _ string) string    { return "" }
-func (m *mockStore) AudioExists(_ context.Context, _ string) bool             { return false }
-func (m *mockStore) PutAudio(_ context.Context, _ string, _ []byte) error     { return nil }
+func (m *mockStore) AudioObjectKey(_ string, _ int, _ string) string       { return "" }
+func (m *mockStore) AudioObjectKeyExt(_ string, _ int, _, _ string) string { return "" }
+func (m *mockStore) AudioExists(_ context.Context, _ string) bool          { return false }
+func (m *mockStore) PutAudio(_ context.Context, _ string, _ []byte) error  { return nil }
 func (m *mockStore) PutAudioStream(_ context.Context, _ string, _ io.Reader, _ int64, _ string) error {
 	return nil
 }

backend/internal/orchestrator/orchestrator_test.go

@@ -89,6 +89,8 @@ func (s *stubStore) WriteChapterRefs(_ context.Context, _ string, _ []domain.Cha
 	return nil
 }
 
+func (s *stubStore) DeduplicateChapters(_ context.Context, _ string) (int, error) { return 0, nil }
+
 func (s *stubStore) ChapterExists(_ context.Context, slug string, ref domain.ChapterRef) bool {
 	s.mu.Lock()
 	defer s.mu.Unlock()

backend/internal/runner/runner_test.go

@@ -94,6 +94,10 @@ func (s *stubBookWriter) ChapterExists(_ context.Context, _ string, _ domain.Cha
 	return false
 }
 
+func (s *stubBookWriter) DeduplicateChapters(_ context.Context, _ string) (int, error) {
+	return 0, nil
+}
+
 // stubBookReader satisfies bookstore.BookReader — returns a single chapter.
 type stubBookReader struct {
 	text    string