Add concurrent anime processing support

- Modified BackgroundLoaderService to use multiple workers (default: 5)
- Anime additions now process in parallel without blocking
- Added comprehensive unit tests for concurrent behavior
- Updated integration tests for compatibility
- Updated architecture documentation

docs/architecture/async_loading_architecture.md

@@ -1,8 +1,41 @@
 # Asynchronous Series Data Loading Architecture
 
-**Version:** 1.0  
-**Date:** 2026-01-18  
-**Status:** Planning Phase
+**Version:** 2.0  
+**Date:** 2026-01-24  
+**Status:** ✅ Implemented with Concurrent Processing
+
+## ⚡ Update 2.0 - Concurrent Processing (2026-01-24)
+
+**Enhancement**: Added support for concurrent processing of multiple anime additions.
+
+###  Changes Made
+
+1. **Multiple Worker Architecture**: 
+   - Changed from single worker to configurable multiple workers (default: 5)
+   - Multiple anime can now be processed simultaneously
+   - Non-blocking queue processing allows immediate response to additional requests
+
+2. **Backward Compatibility**:
+   - All existing APIs remain unchanged
+   - Drop-in replacement for single-worker implementation
+   - Tests updated to reflect concurrent behavior
+
+3. **Configuration**:
+   - `max_concurrent_loads` parameter added to control worker count
+   - Default set to 5 concurrent loads for optimal balance
+
+4. **Performance Impact**:
+   - Multiple anime additions now process in parallel
+   - No blocking when adding second anime while first is loading
+   - Each worker processes tasks independently from queue
+
+### Migration Notes
+
+- **Attribute Change**: `worker_task` → `worker_tasks` (now a list)
+- **Stop Behavior**: Gracefully stops all workers with proper cleanup
+- **Tests**: Updated to verify concurrent processing
+
+---
 
 ## Table of Contents