feat: migrate to PostgreSQL and enhance playlist curation

- Migrate database from SQLite to PostgreSQL (100.91.248.114:5433)
- Fix playlist curation to use actual top tracks instead of AI name matching
- Add /playlists/history endpoint for historical playlist viewing
- Add Playlist Archives section to frontend with expandable history
- Add playlist-modify-* scopes to Spotify OAuth for playlist creation
- Rewrite Genius client to use official API (fixes 403 scraping blocks)
- Ensure playlists are created on Spotify before curation attempts
- Add DATABASE.md documentation for PostgreSQL schema
- Add migrations for PlaylistConfig and composition storage

backend/Dockerfile

@@ -3,9 +3,10 @@ FROM python:3.11-slim
 
 WORKDIR /app
 
-# Install system dependencies
+# Install system dependencies (including PostgreSQL client libs for psycopg2)
 RUN apt-get update && apt-get install -y --no-install-recommends \
     curl \
+    libpq-dev \
     && rm -rf /var/lib/apt/lists/*
 
 COPY requirements.txt .