fix: remove auto-appending of /RPC2 from RTorrentClient and finalize PDCA documentation

- Remove auto-appending of /RPC2 from RTorrentClient constructor
- Use exact URL from config (supports custom paths like whatbox.ca/xmlrpc)
- Update .env.sample with clear URL path documentation and examples
- Update README.md with comprehensive PDCA section and all download clients
- Add URL path verification tests (whatbox.ca, custom paths, no auth)
- Update architecture diagram to include Transmission and rTorrent
- Update Docker Compose example to include all download clients
- Update prerequisites to mention all supported download clients
- Update "What It Does" and "The Matching Process" sections

README.md

@@ -7,7 +7,7 @@
 ## What It Does
 
 sofarr connects to your media stack and shows you a personalized view of:
-- **Active Downloads** - See what's currently downloading from Usenet (SABnzbd) and BitTorrent (qBittorrent)
+- **Active Downloads** - See what's currently downloading from Usenet (SABnzbd) and BitTorrent (qBittorrent, Transmission, rTorrent)
 - **Progress Tracking** - Real-time progress bars with speed, ETA, and completion estimates
 - **Recently Completed** - History tab showing imported and failed downloads from Sonarr/Radarr with deduplication and upgrade-awareness
 - **User Matching** - Downloads are matched to you based on tags in Sonarr/Radarr
@@ -21,7 +21,9 @@ sofarr connects to your media stack and shows you a personalized view of:
 ┌─────────────┐     ┌──────────────┐     ┌─────────────────────────────┐
 │   Browser   │────▶│   sofarr     │────▶│  SABnzbd (Usenet downloads)   │
 │   (User)    │◀────│   Server     │     │  qBittorrent (Torrents)       │
-└─────────────┘     └──────────────┘     │  Sonarr (TV management)       │
+└─────────────┘     └──────────────┘     │  Transmission (Torrents)      │
+                       │                 │  rTorrent (Torrents)          │
+                       │                 │  Sonarr (TV management)       │
                        │                 │  Radarr (Movie management)    │
                        │                 │  Emby (User authentication)   │
                        ▼                 └─────────────────────────────┘
@@ -34,10 +36,10 @@ sofarr connects to your media stack and shows you a personalized view of:
 ### The Matching Process
 
 1. **User Authentication**: Login via Emby credentials
-2. **Tag-Based Matching**: 
+2. **Tag-Based Matching**:
    - Your media in Sonarr/Radarr is tagged with your username (e.g., "gordon")
    - sofarr checks Sonarr/Radarr activity to find items tagged with your name
-   - Downloads (from SABnzbd/qBittorrent) are matched by title to that activity
+   - Downloads (from SABnzbd, qBittorrent, Transmission, or rTorrent) are matched by title to that activity
    - Only your downloads appear on your dashboard
 
 ### Multi-Instance Support
@@ -53,7 +55,7 @@ SONARR_INSTANCES=[{"name":"main","url":"...","apiKey":"..."}]
 ## Prerequisites
 
 - **Docker** (recommended), or Node.js (v22+) for manual installation
-- At least one of: SABnzbd or qBittorrent
+- At least one download client: SABnzbd, qBittorrent, Transmission, or rTorrent
 - Sonarr (optional, for TV tracking)
 - Radarr (optional, for movie tracking)
 - Emby (for user authentication)
@@ -108,6 +110,8 @@ docker run -d \
   -e RADARR_INSTANCES='[{"name":"main","url":"http://radarr:7878","apiKey":"your-key"}]' \
   -e SABNZBD_INSTANCES='[{"name":"main","url":"http://sabnzbd:8080","apiKey":"your-key"}]' \
   -e QBITTORRENT_INSTANCES='[{"name":"main","url":"http://qbit:8080","username":"admin","password":"pass"}]' \
+  -e TRANSMISSION_INSTANCES='[{"name":"main","url":"http://transmission:9091","username":"admin","password":"pass"}]' \
+  -e RTORRENT_INSTANCES='[{"name":"main","url":"http://rtorrent:8080/RPC2","username":"rtorrent","password":"rtorrent"}]' \
   -e LOG_LEVEL=info \
   -e POLL_INTERVAL=5000 \
   docker.i3omb.com/sofarr:latest
@@ -131,6 +135,8 @@ services:
       - RADARR_INSTANCES=[{"name":"main","url":"http://radarr:7878","apiKey":"your-key"}]
       - SABNZBD_INSTANCES=[{"name":"main","url":"http://sabnzbd:8080","apiKey":"your-key"}]
       - QBITTORRENT_INSTANCES=[{"name":"main","url":"http://qbit:8080","username":"admin","password":"pass"}]
+      - TRANSMISSION_INSTANCES=[{"name":"main","url":"http://transmission:9091","username":"admin","password":"pass"}]
+      - RTORRENT_INSTANCES=[{"name":"main","url":"http://rtorrent:8080/RPC2","username":"rtorrent","password":"rtorrent"}]
       - LOG_LEVEL=info
       - POLL_INTERVAL=5000
 ```
@@ -188,6 +194,19 @@ POLL_INTERVAL=5000                  # Background polling interval in ms (default
                                     # Set to 0 or "off" to disable (on-demand mode)
 ```
 
+### Download Clients (PDCA)
+
+sofarr uses a **Pluggable Download Client Architecture (PDCA)** that provides a unified interface for all download clients. This enables consistent data normalization, easy addition of new client types, and centralized configuration management.
+
+**Supported Download Clients:**
+
+| Client | Protocol | Auth Method | Notes |
+|--------|----------|-------------|-------|
+| SABnzbd | REST API | API Key | Usenet downloads |
+| qBittorrent | Sync API | Username/Password | BitTorrent with incremental updates |
+| Transmission | JSON-RPC | Username/Password | BitTorrent with session management |
+| rTorrent | XML-RPC | HTTP Basic Auth | BitTorrent, requires full endpoint path |
+
 ### Service Instances (JSON Array Format)
 
 All services support multi-instance configuration via single-line JSON arrays:
@@ -199,10 +218,20 @@ SABNZBD_INSTANCES=[{"name":"primary","url":"https://sabnzbd.example.com","apiKey
 # qBittorrent Instances (uses username/password, not API key)
 QBITTORRENT_INSTANCES=[{"name":"main","url":"https://qbittorrent.example.com","username":"admin","password":"secret"}]
 
+# Transmission Instances (uses username/password)
+TRANSMISSION_INSTANCES=[{"name":"main","url":"http://transmission:9091/transmission/rpc","username":"admin","password":"pass"}]
+
+# rTorrent Instances (uses username/password, URL must include full RPC endpoint)
+# Standard installs use /RPC2. Some providers like whatbox.ca use /xmlrpc.
+RTORRENT_INSTANCES=[{"name":"main","url":"http://rtorrent:8080/RPC2","username":"rtorrent","password":"rtorrent"}]
+
+# For whatbox.ca (example):
+# RTORRENT_INSTANCES=[{"name":"whatbox","url":"https://user.whatbox.ca/xmlrpc","username":"user","password":"pass"}]
+
 # Sonarr Instances
 SONARR_INSTANCES=[{"name":"hd","url":"https://sonarr.example.com","apiKey":"your-api-key"}]
 
-# Radarr Instances  
+# Radarr Instances
 RADARR_INSTANCES=[{"name":"movies","url":"https://radarr.example.com","apiKey":"your-api-key"}]
 
 # Emby (single instance for authentication)
@@ -216,6 +245,18 @@ If you only have one instance, you can use the legacy format:
 ```bash
 SABNZBD_URL=https://sabnzbd.example.com
 SABNZBD_API_KEY=your-api-key
+
+QBITTORRENT_URL=https://qbittorrent.example.com
+QBITTORRENT_USERNAME=admin
+QBITTORRENT_PASSWORD=secret
+
+TRANSMISSION_URL=http://transmission:9091/transmission/rpc
+TRANSMISSION_USERNAME=admin
+TRANSMISSION_PASSWORD=pass
+
+RTORRENT_URL=http://rtorrent:8080/RPC2
+RTORRENT_USERNAME=rtorrent
+RTORRENT_PASSWORD=rtorrent
 ```
 
 ## Setting Up User Tags