Fix Issue 7: Enforce repository pattern consistency

- Added 5 new service methods for complete database coverage:
  * get_series_without_nfo()
  * count_all()
  * count_with_nfo()
  * count_with_tmdb_id()
  * count_with_tvdb_id()

- Eliminated all direct database queries from business logic:
  * series_manager_service.py - now uses AnimeSeriesService
  * anime_service.py - now uses service layer methods

- Documented architecture decision in ARCHITECTURE.md:
  * Service layer IS the repository layer
  * No direct SQLAlchemy queries allowed outside service layer

- All database access must go through service methods
- 1449 tests passing, repository pattern enforced

docs/ARCHITECTURE.md

@@ -376,19 +376,54 @@ Source: [src/server/api/websocket.py](../src/server/api/websocket.py#L1-L260)
 
 ## 4. Design Patterns
 
-### 4.1 Repository Pattern
+### 4.1 Repository Pattern (Service Layer as Repository)
 
-Database access is abstracted through repository classes.
+**Architecture Decision**: The Service Layer serves as the Repository layer for database access.
+
+Database access is abstracted through service classes in `src/server/database/service.py` that provide CRUD operations and act as the repository layer. This eliminates the need for a separate repository layer while maintaining clean separation of concerns.
+
+**Service Layer Classes** (acting as repositories):
+
+- `AnimeSeriesService` - CRUD operations for anime series
+- `EpisodeService` - CRUD operations for episodes
+- `DownloadQueueService` - CRUD operations for download queue
+- `UserSessionService` - CRUD operations for user sessions
+- `SystemSettingsService` - CRUD operations for system settings
+
+**Key Principles**:
+
+1. **No Direct Database Queries**: Controllers and business logic services MUST use service layer methods
+2. **Service Layer Encapsulation**: All SQLAlchemy queries are encapsulated in service methods
+3. **Consistent Interface**: Services provide consistent async methods for all database operations
+4. **Single Responsibility**: Each service manages one entity type
+
+**Example Usage**:
 
 ```python
-# QueueRepository provides CRUD for download items
+# CORRECT: Use service layer
+from src.server.database.service import AnimeSeriesService
+
+async with get_db_session() as db:
+    series = await AnimeSeriesService.get_by_key(db, "attack-on-titan")
+    await AnimeSeriesService.update(db, series.id, has_nfo=True)
+
+# INCORRECT: Direct database query
+result = await db.execute(select(AnimeSeries).filter(...))  # ❌ Never do this
+```
+
+**Special Case - Queue Repository Adapter**:
+
+The `QueueRepository` in `src/server/services/queue_repository.py` is an adapter that wraps `DownloadQueueService` to provide domain model conversion between Pydantic models and SQLAlchemy models:
+
+```python
+# QueueRepository provides CRUD with model conversion
 class QueueRepository:
-    async def save_item(self, item: DownloadItem) -> None: ...
-    async def get_all_items(self) -> List[DownloadItem]: ...
+    async def save_item(self, item: DownloadItem) -> None: ...  # Converts Pydantic → SQLAlchemy
+    async def get_all_items(self) -> List[DownloadItem]: ...    # Converts SQLAlchemy → Pydantic
     async def delete_item(self, item_id: str) -> bool: ...
 ```
 
-Source: [src/server/services/queue_repository.py](../src/server/services/queue_repository.py)
+Source: [src/server/database/service.py](../src/server/database/service.py), [src/server/services/queue_repository.py](../src/server/services/queue_repository.py)
 
 ### 4.2 Dependency Injection