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

docs/research/melodee/README.md

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+# Melodee
+
+## Overview
+
+Industrial-grade self-hosted streaming music server. Comprehensive music management and streaming system with metadata enrichment from multiple sources.
+
+## Key Features
+
+- **Stars**: 62
+- **APIs**: OpenSubsonic, Jellyfin API, Native REST API
+- **Metadata Sources**: MusicBrainz (local cache), Last.fm, Spotify, iTunes, Deezer
+- **Formats**: AAC, AC3, M4A, FLAC, OGG, APE, MP3, WAV, WMA, and more
+- **License**: MIT
+
+## Source
+
+| Resource | URL |
+|----------|-----|
+| **Repository** | https://github.com/melodee-project/melodee |
+| **Website** | https://melodee.org |
+| **Documentation** | https://melodee.org/docs |
+
+## Architecture
+
+Multi-stage pipeline:
+1. **Inbound** - Scan detects new files
+2. **Ingestion** - Convert, normalize tags, apply cleanup rules
+3. **Staging** - Optional manual curation
+4. **Storage** - Publish to libraries
+5. **Indexed** - Fast search and streaming via APIs
+
+## Tech Stack
+
+- **Language**: C# (.NET 10)
+- **UI**: Blazor (Radzen components)
+- **Scheduling**: Quartz.NET
+- **Database**: PostgreSQL
+
+## APIs
+
+- **OpenSubsonic** - Compatible with Subsonic clients
+- **Jellyfin API** - Compatible with Finamp, Feishin, Streamyfin
+- **Native REST** - `/scalar/v1` with OpenAPI spec at `/openapi/v1.json`
+
+## Self-Hosting
+
+```bash
+docker pull ghcr.io/melodee-project/melodee:latest
+docker run -p 8080:8080 -v /path/to/music:/music melodee
+```
+
+## Notes
+
+- Designed for homelab (runs on Raspberry Pi to full servers)
+- MusicBrainz local cache with monthly updates
+- Real-time transcoding (MP3, Ogg, Opus)
+- Scrobbling support (Last.fm)