docs: add SetupService to architecture, update changelog and testing docs

- ARCHITECTURE.md: add setup_service.py to services list
- CHANGELOG.md: add Unreleased section with folder scan key resolution fix
- TESTING.md: add SetupService testing section with example tests

docs/TESTING.md

@@ -73,40 +73,31 @@ from src.server.models.download import DownloadItem, EpisodeIdentifier
 class MockQueueRepository:
     def __init__(self):
         self._items: Dict[str, DownloadItem] = {}
-
-    async def save_item(self, item: DownloadItem) -> DownloadItem:
-        self._items[item.id] = item
-        return item
-
-    async def get_item(self, item_id: str) -> Optional[DownloadItem]:
-        return self._items.get(item_id)
-
-    async def get_all_items(self) -> List[DownloadItem]:
-        return list(self._items.values())
-
-    async def set_error(self, item_id: str, error: str) -> bool:
-        if item_id in self._items:
-            self._items[item_id].error = error
-            return True
-        return False
-
-    async def delete_item(self, item_id: str) -> bool:
-        if item_id in self._items:
-            del self._items[item_id]
-            return True
-        return False
-
-    async def clear_all(self) -> int:
-        count = len(self._items)
-        self._items.clear()
-        return count
 ```
 
-**Key points:**
-- The mock uses in-memory storage, no database required
-- All async methods are implemented (even if just pass-through)
-- `save_item` uses `item.id` as key (must be set before calling)
-- Suitable for unit tests only (no persistence)
+### Testing SetupService
+
+SetupService handles series key resolution from folder names during library setup. Test file: `tests/unit/test_setup_service.py`.
+
+Key methods tested:
+- `_extract_year_from_folder_name()` — parses `(YYYY)` suffix
+- `_extract_title_from_folder_name()` — strips year suffix
+- `_resolve_key_via_search()` — resolves provider key via fuzzy title matching
+
+```python
+@pytest.mark.asyncio
+async def test_returns_key_when_single_exact_match(self):
+    """Search returns 1 result with same name → returns key."""
+    mock_series_app = AsyncMock()
+    mock_series_app.search.return_value = [
+        {'title': 'Attack on Titan', 'link': '/anime/stream/attack-on-titan'}
+    ]
+
+    with patch('src.server.services.setup_service.get_series_app', return_value=mock_series_app):
+        result = await SetupService._resolve_key_via_search("Attack on Titan")
+
+    assert result == 'attack-on-titan'
+```
 
 ### Mocking aiohttp Sessions