feat: initial implementation of metadata aggregator

- gRPC service with MusicBrainz provider
- PostgreSQL schema with migrations
- Service layer with database-first caching
- Repository pattern for data access
- YAML configuration support
- Research documentation for 17 music metadata projects

cmd/server/noop_repo.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"context"
+
+	"github.com/metadata-agregator/internal/domain"
+	"github.com/metadata-agregator/internal/repository"
+)
+
+type noopArtistRepo struct{}
+
+func (r *noopArtistRepo) GetByID(ctx context.Context, id string) (*domain.Artist, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopArtistRepo) GetByExternalID(ctx context.Context, source, sourceID string) (*domain.Artist, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopArtistRepo) Search(ctx context.Context, query string, limit, offset int) (*domain.SearchResult[domain.Artist], error) {
+	return &domain.SearchResult[domain.Artist]{}, nil
+}
+
+func (r *noopArtistRepo) Save(ctx context.Context, artist *domain.Artist) error {
+	return nil
+}
+
+type noopAlbumRepo struct{}
+
+func (r *noopAlbumRepo) GetByID(ctx context.Context, id string) (*domain.Album, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopAlbumRepo) GetByExternalID(ctx context.Context, source, sourceID string) (*domain.Album, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopAlbumRepo) GetByArtistID(ctx context.Context, artistID string, limit, offset int) (*domain.SearchResult[domain.Album], error) {
+	return &domain.SearchResult[domain.Album]{}, nil
+}
+
+func (r *noopAlbumRepo) Save(ctx context.Context, album *domain.Album) error {
+	return nil
+}
+
+type noopTrackRepo struct{}
+
+func (r *noopTrackRepo) GetByID(ctx context.Context, id string) (*domain.Track, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopTrackRepo) GetByExternalID(ctx context.Context, source, sourceID string) (*domain.Track, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopTrackRepo) GetByISRC(ctx context.Context, isrc string) (*domain.Track, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopTrackRepo) GetByAlbumID(ctx context.Context, albumID string) ([]domain.Track, error) {
+	return nil, nil
+}
+
+func (r *noopTrackRepo) Save(ctx context.Context, track *domain.Track) error {
+	return nil
+}