feat: add rtorrent client via PDCA

- Implement RTorrentClient extending DownloadClient abstract class
- Use xmlrpc package (v1.3.2) for XML-RPC communication
- Support HTTP Basic Auth when credentials are configured
- Map rTorrent states (d.state, d.is_active, d.is_hash_checking) to normalized statuses
- Calculate ETA from download speed and remaining bytes
- Add getRtorrentInstances() to config.js
- Register RTorrentClient in downloadClients.js registry
- Add 8 comprehensive unit tests covering all functionality
- Update .env.sample with rtorrent configuration examples
- Update ARCHITECTURE.md with rtorrent client details
- Update ADDING-A-DOWNLOAD-CLIENT.md with rtorrent-specific notes

server/utils/config.js

@@ -104,12 +104,23 @@ function getTransmissionInstances() {
   );
 }
 
+function getRtorrentInstances() {
+  return parseInstances(
+    process.env.RTORRENT_INSTANCES,
+    process.env.RTORRENT_URL,
+    null, // no apiKey for rtorrent
+    process.env.RTORRENT_USERNAME,
+    process.env.RTORRENT_PASSWORD
+  );
+}
+
 module.exports = {
   getSABnzbdInstances,
   getSonarrInstances,
   getRadarrInstances,
   getQbittorrentInstances,
   getTransmissionInstances,
+  getRtorrentInstances,
   parseInstances,
   validateInstanceUrl
 };

server/utils/downloadClients.js

@@ -3,19 +3,22 @@ const { logToFile } = require('./logger');
 const {
   getSABnzbdInstances,
   getQbittorrentInstances,
-  getTransmissionInstances
+  getTransmissionInstances,
+  getRtorrentInstances
 } = require('./config');
 
 // Import client classes
 const SABnzbdClient = require('../clients/SABnzbdClient');
 const QBittorrentClient = require('../clients/QBittorrentClient');
 const TransmissionClient = require('../clients/TransmissionClient');
+const RTorrentClient = require('../clients/RTorrentClient');
 
 // Client type mapping
 const clientClasses = {
   sabnzbd: SABnzbdClient,
   qbittorrent: QBittorrentClient,
-  transmission: TransmissionClient
+  transmission: TransmissionClient,
+  rtorrent: RTorrentClient
 };
 
 /**
@@ -41,12 +44,14 @@ class DownloadClientRegistry {
     const sabnzbdInstances = getSABnzbdInstances();
     const qbittorrentInstances = getQbittorrentInstances();
     const transmissionInstances = getTransmissionInstances();
+    const rtorrentInstances = getRtorrentInstances();
 
     // Create client instances
     const instanceConfigs = [
       ...sabnzbdInstances.map(inst => ({ ...inst, type: 'sabnzbd' })),
       ...qbittorrentInstances.map(inst => ({ ...inst, type: 'qbittorrent' })),
-      ...transmissionInstances.map(inst => ({ ...inst, type: 'transmission' }))
+      ...transmissionInstances.map(inst => ({ ...inst, type: 'transmission' })),
+      ...rtorrentInstances.map(inst => ({ ...inst, type: 'rtorrent' }))
     ];
 
     for (const config of instanceConfigs) {