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

go.mod

@@ -0,0 +1,24 @@
+module github.com/metadata-agregator
+
+go 1.25.0
+
+require (
+	github.com/jackc/pgx/v5 v5.9.2
+	golang.org/x/time v0.15.0
+	google.golang.org/grpc v1.68.0
+	google.golang.org/protobuf v1.35.2
+	gopkg.in/yaml.v3 v3.0.1
+)
+
+require (
+	github.com/jackc/pgpassfile v1.0.0 // indirect
+	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
+	github.com/jackc/puddle/v2 v2.2.2 // indirect
+	github.com/kr/text v0.2.0 // indirect
+	github.com/rogpeppe/go-internal v1.14.1 // indirect
+	golang.org/x/net v0.29.0 // indirect
+	golang.org/x/sync v0.17.0 // indirect
+	golang.org/x/sys v0.26.0 // indirect
+	golang.org/x/text v0.29.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20240903143218-8af14fe29dc1 // indirect
+)