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/bookstore/bookstore.go

@@ -105,6 +105,10 @@ type PresignStore interface {
 	// Returns ("", false, nil) when no avatar exists.
 	PresignAvatarURL(ctx context.Context, userID string) (string, bool, error)
 
+	// PutAvatar stores raw image bytes for a user avatar directly in MinIO.
+	// ext should be "jpg", "png", or "webp". Returns the object key.
+	PutAvatar(ctx context.Context, userID, ext, contentType string, data []byte) (key string, err error)
+
 	// DeleteAvatar removes all avatar objects for a user.
 	DeleteAvatar(ctx context.Context, userID string) error
 }
@@ -124,14 +128,16 @@ type ProgressStore interface {
 	DeleteProgress(ctx context.Context, sessionID, slug string) error
 }
 
-// BrowseStore covers browse page snapshot storage.
-// The runner writes snapshots; the backend reads them.
-type BrowseStore interface {
-	// PutBrowsePage stores a raw JSON snapshot for a browse page.
-	// genre, sort, status, novelType and page identify the page.
-	PutBrowsePage(ctx context.Context, genre, sort, status, novelType string, page int, data []byte) error
+// CoverStore covers book cover image storage in MinIO.
+// The runner writes covers during catalogue refresh; the backend reads them.
+type CoverStore interface {
+	// PutCover stores a raw cover image for a book identified by slug.
+	PutCover(ctx context.Context, slug string, data []byte, contentType string) error
 
-	// GetBrowsePage retrieves a raw JSON snapshot. Returns (nil, false, nil)
-	// when no snapshot exists for the given parameters.
-	GetBrowsePage(ctx context.Context, genre, sort, status, novelType string, page int) ([]byte, bool, error)
+	// GetCover retrieves the cover image for a book. Returns (nil, false, nil)
+	// when no cover exists for the given slug.
+	GetCover(ctx context.Context, slug string) ([]byte, string, bool, error)
+
+	// CoverExists returns true when a cover image is stored for slug.
+	CoverExists(ctx context.Context, slug string) bool
 }

backend/internal/bookstore/bookstore_test.go

@@ -68,6 +68,9 @@ func (m *mockStore) PresignAvatarUpload(_ context.Context, _, _ string) (string,
 func (m *mockStore) PresignAvatarURL(_ context.Context, _ string) (string, bool, error) {
 	return "", false, nil
 }
+func (m *mockStore) PutAvatar(_ context.Context, _, _, _ string, _ []byte) (string, error) {
+	return "", nil
+}
 func (m *mockStore) DeleteAvatar(_ context.Context, _ string) error { return nil }
 
 // ProgressStore