feat: add artist sync flow and stub torrent client

- Add DownloadService to orchestrate metadata → indexer → torrent flow
- Add POST /api/sync/artist endpoint for syncing artist albums
- Add StubTorrentClient for testing (logs requests to file)
- Refactor TorrentConfig to tagged enum (client_type: qbittorrent|stub|none)
- Add POST /api/reload endpoint for hot config reload
- Add chrono dependency for timestamps

src/main.rs

@@ -54,23 +54,25 @@ async fn main() {
         }
     };
 
-    let torrent_service = if let Some(qbit_config) = &config.torrent.qbittorrent {
-        match TorrentService::from_qbittorrent_config(qbit_config).await {
-            Ok(svc) => {
-                tracing::info!("connected to qBittorrent at {}", qbit_config.url);
-                svc
-            }
-            Err(e) => {
-                tracing::warn!(
-                    "failed to connect to qBittorrent: {} (continuing without torrent client)",
-                    e
-                );
-                TorrentService::new()
+    let torrent_service = match TorrentService::from_config(&config.torrent).await {
+        Ok(svc) => {
+            match &config.torrent {
+                config::TorrentConfig::QBittorrent { url, .. } => {
+                    tracing::info!("connected to qBittorrent at {}", url);
+                }
+                config::TorrentConfig::Stub { log_path, .. } => {
+                    tracing::info!("using stub torrent client, logging to {}", log_path);
+                }
+                config::TorrentConfig::None => {
+                    tracing::info!("no torrent client configured");
+                }
             }
+            svc
+        }
+        Err(e) => {
+            tracing::warn!("failed to init torrent client: {} (continuing without)", e);
+            TorrentService::new()
         }
-    } else {
-        tracing::info!("no torrent client configured");
-        TorrentService::new()
     };
 
     let mut metadata_service = MetadataService::new(&config.metadata.endpoint);
@@ -93,6 +95,7 @@ async fn main() {
         indexer_service,
         torrent_service,
         metadata_service,
+        args.config.clone(),
     )));
 
     let cors = CorsLayer::new()