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/minim/README.md

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+# minim
+
+## Overview
+
+A lightweight Python library providing unified client interface to 7 music service APIs for media information retrieval and semi-automated music tagging.
+
+## Key Features
+
+- **APIs**: Deezer, Discogs, iTunes, Musixmatch, Qobuz, Spotify, TIDAL
+- **Purpose**: Unified interface for metadata retrieval
+- **Tagging**: Semi-automated music file tagging
+- **License**: MIT
+
+## Source
+
+| Resource | URL |
+|----------|-----|
+| **Repository** | https://github.com/bbye98/minim |
+| **Documentation** | https://bbye98.github.io/minim |
+| **PyPI** | https://pypi.org/project/minim |
+
+## Modules
+
+- `minim.audio` - Audio file handlers for reading/writing metadata
+- `minim.discogs` - Discogs API client (OAuth support)
+- `minim.itunes` - iTunes Search API client
+- `minim.qobuz` - Qobuz API client (password auth)
+- `minim.spotify` - Spotify Web API client (multiple grant types)
+- `minim.tidal` - TIDAL API client (old and new APIs)
+
+## Usage Example
+
+```python
+from minim import spotify, itunes, tidal
+
+# Search across services
+client_spotify = spotify.WebAPI()
+result = client_spotify.search("Galantis", "artist", limit=1)
+
+client_itunes = itunes.SearchAPI()
+result = client_itunes.search("Galantis", entity="musicArtist", limit=1)
+
+client_tidal = tidal.API()
+result = client_tidal.search("Galantis", type="artist", limit=1)
+```
+
+## Installation
+
+```bash
+pip install minim
+```
+
+## Notes
+
+- Unified Python interface to multiple services
+- OAuth support with token caching
+- Audio format conversion support
+- Best for building Python applications that need multi-source lookup