feat: spotify playlist injection

- Add SpotifyImportSettings configuration model
- Create SpotifyMissingTracksFetcher background service
- Inject virtual Spotify playlists into search results
- Auto-match tracks from external providers
- Update README with feature documentation
- Configure sync window and playlist settings

allstarr/appsettings.json

@@ -3,7 +3,7 @@
     "Type": "Subsonic"
   },
   "Subsonic": {
-    "Url": "https://navidrome.local.bransonb.com",
+    "Url": "http://localhost:4533",
     "MusicService": "SquidWTF",
     "ExplicitFilter": "All",
     "DownloadMode": "Track",
@@ -42,5 +42,25 @@
   "Redis": {
     "Enabled": true,
     "ConnectionString": "localhost:6379"
+  },
+  "SpotifyImport": {
+    "Enabled": false,
+    "JellyfinUrl": "https://jellyfin.example.com",
+    "ApiKey": "",
+    "SyncStartHour": 16,
+    "SyncStartMinute": 15,
+    "SyncWindowHours": 2,
+    "Playlists": [
+      {
+        "Name": "Release Radar",
+        "SpotifyName": "Release Radar",
+        "Enabled": true
+      },
+      {
+        "Name": "Discover Weekly",
+        "SpotifyName": "Discover Weekly",
+        "Enabled": true
+      }
+    ]
   }
 }