feat: scaffold FastAPI backend with ports-and-adapters layout

backend/app/domain/profile.py

@@ -0,0 +1,12 @@
+"""Taste-profile compression: raw listening data to a prompt-sized summary."""
+
+from app.domain.models import TasteProfile
+
+
+def compress_taste_profile(profile: TasteProfile, artist_limit: int = 15) -> str:
+    """Render a profile as compact prompt text, bounded in size."""
+    return (
+        f"Top artists (long term): {', '.join(profile.top_artists_long_term[:artist_limit])}. "
+        f"Top artists (recent): {', '.join(profile.top_artists_short_term[:artist_limit])}. "
+        f"Recent favourite tracks: {', '.join(profile.top_tracks_short_term[:artist_limit])}."
+    )