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/app/services/narrative_service.py

@@ -119,6 +119,7 @@ class NarrativeService:
 2. Provide a "description" (2-3 sentences explaining why).
 3. Identify 10-15 "curated_tracks" (song names only) that fit this vibe and the artists listed.
 4. Return ONLY valid JSON.
+5. Do NOT output internal variable names (e.g. 'part_of_day', 'avg_valence') in the description. Translate them to natural language (e.g. 'morning listens', 'happy vibe').
 
 **REQUIRED JSON:**
 {{
@@ -192,6 +193,7 @@ class NarrativeService:
 2. Be specific - reference actual metrics from the data.
 3. Be playful but not cruel.
 4. Return ONLY valid JSON.
+5. Translate all technical metrics (e.g. 'discovery_rate', 'valence', 'hhi') into natural language descriptions. Do NOT use the variable names themselves.
 
 **LISTENING HIGHLIGHTS:**
 - Peak listening: {peak_listening}