Complete Phase 7: Testing and Validation for identifier standardization

- Task 7.1: Update All Test Fixtures to Use Key
  - Updated FakeSerie/FakeSeriesApp with realistic keys in test_anime_endpoints.py
  - Updated 6+ fixtures in test_websocket_integration.py
  - Updated 5 fixtures in test_download_progress_integration.py
  - Updated 9 fixtures in test_download_progress_websocket.py
  - Updated 10+ fixtures in test_download_models.py
  - All fixtures now use URL-safe, lowercase, hyphenated key format

- Task 7.2: Add Integration Tests for Identifier Consistency
  - Created tests/integration/test_identifier_consistency.py with 10 tests
  - TestAPIIdentifierConsistency: API response validation
  - TestServiceIdentifierConsistency: Download service key usage
  - TestWebSocketIdentifierConsistency: WebSocket events
  - TestIdentifierValidation: Model validation
  - TestEndToEndIdentifierFlow: Full flow verification
  - Tests use UUID suffixes for isolation

All 1006 tests passing.

tests/api/test_anime_endpoints.py

@@ -10,10 +10,25 @@ from src.server.services.auth_service import auth_service
 
 
 class FakeSerie:
-    """Mock Serie object for testing."""
+    """Mock Serie object for testing.
+    
+    Note on identifiers:
+    - key: Provider-assigned URL-safe identifier (e.g., 'attack-on-titan')
+    - folder: Filesystem folder name for metadata only (e.g., 'Attack on Titan (2013)')
+    
+    The 'key' is the primary identifier used for all lookups and operations.
+    The 'folder' is metadata only, not used for identification.
+    """
 
     def __init__(self, key, name, folder, episodeDict=None):
-        """Initialize fake serie."""
+        """Initialize fake serie.
+        
+        Args:
+            key: Provider-assigned URL-safe key (primary identifier)
+            name: Display name for the series
+            folder: Filesystem folder name (metadata only)
+            episodeDict: Dictionary of missing episodes
+        """
         self.key = key
         self.name = name
         self.folder = folder
@@ -28,8 +43,9 @@ class FakeSeriesApp:
         """Initialize fake series app."""
         self.list = self  # Changed from self.List to self.list
         self._items = [
-            FakeSerie("1", "Test Show", "test_show", {1: [1, 2]}),
-            FakeSerie("2", "Complete Show", "complete_show", {}),
+            # Using realistic key values (URL-safe, lowercase, hyphenated)
+            FakeSerie("test-show-key", "Test Show", "Test Show (2023)", {1: [1, 2]}),
+            FakeSerie("complete-show-key", "Complete Show", "Complete Show (2022)", {}),
         ]
 
     def GetMissingEpisode(self):
@@ -120,9 +136,15 @@ def test_list_anime_direct_call():
 
 
 def test_get_anime_detail_direct_call():
-    """Test get_anime function directly."""
+    """Test get_anime function directly.
+    
+    Uses the series key (test-show-key) for lookup, not the folder name.
+    """
     fake = FakeSeriesApp()
-    result = asyncio.run(anime_module.get_anime("1", series_app=fake))
+    # Use the series key (primary identifier) for lookup
+    result = asyncio.run(
+        anime_module.get_anime("test-show-key", series_app=fake)
+    )
     assert result.title == "Test Show"
     assert "1-1" in result.episodes