feat(wave): implement Phase 1 Smart Wave recommendations and buffer rotation

app/wave/playlist.py

@@ -0,0 +1,42 @@
+import os
+import json
+from app.config import settings
+
+def ensure_smart_playlist(playlist_name: str = "Моя Волна") -> str:
+    """Ensure Navidrome .nsp Smart Playlist exists in library."""
+    playlists_dir = os.path.join(settings.MUSIC_DIR, "playlists")
+    os.makedirs(playlists_dir, exist_ok=True)
+    
+    nsp_path = os.path.join(playlists_dir, f"{playlist_name}.nsp")
+    
+    # Path inside Navidrome is relative to /music
+    nsp_content = {
+        "all": [
+            {
+                "path": {
+                    "contains": "AI Recommendations/Моя Волна"
+                }
+            }
+        ],
+        "sort": "random",
+        "limit": 100
+    }
+    
+    with open(nsp_path, "w", encoding="utf-8") as f:
+        json.dump(nsp_content, f, ensure_ascii=False, indent=2)
+
+    # Also generate M3U8 playlist at music root for universal Subsonic auto-import
+    wave_dir = os.path.join(settings.MUSIC_DIR, "AI Recommendations", "Моя Волна")
+    m3u_path = os.path.join(settings.MUSIC_DIR, f"{playlist_name}.m3u8")
+    
+    lines = ["#EXTM3U\n"]
+    if os.path.exists(wave_dir):
+        for f in sorted(os.listdir(wave_dir)):
+            if f.lower().endswith(".mp3"):
+                lines.append(f"#EXTINF:-1,{os.path.splitext(f)[0]}\n")
+                lines.append(f"AI Recommendations/Моя Волна/{f}\n")
+
+    with open(m3u_path, "w", encoding="utf-8") as f:
+        f.writelines(lines)
+        
+    return nsp_path