fix: prevent duplicate year suffixes in series name and folder creation

Apply the same duplicate-year prevention logic to additional code paths:

- Serie.name_with_year property: skip adding year suffix if name already ends with it
- add_series API endpoint: avoid duplicating year in folder_name_with_year
- Add integration test for Serie.name_with_year idempotency
- Add API test for add_series endpoint year deduplication

Complements the folder_rename_service fix for comprehensive coverage.

src/core/entities/series.py

@@ -271,7 +271,10 @@ class Serie:
             'Dororo (2025)'
         """
         if self._year:
-            return f"{self._name} ({self._year})"
+            year_suffix = f" ({self._year})"
+            if self._name.endswith(year_suffix):
+                return self._name
+            return f"{self._name}{year_suffix}"
         return self._name
 
     @property

src/server/api/anime.py

@@ -730,7 +730,11 @@ async def add_series(
         
         # Create folder name with year if available
         if year:
-            folder_name_with_year = f"{name} ({year})"
+            year_suffix = f" ({year})"
+            if name.endswith(year_suffix):
+                folder_name_with_year = name
+            else:
+                folder_name_with_year = f"{name}{year_suffix}"
         else:
             folder_name_with_year = name
         

tests/api/test_anime_endpoints.py

@@ -334,6 +334,25 @@ async def test_add_series_sanitizes_folder_name(authenticated_client):
     assert "?" not in folder
 
 
+@pytest.mark.asyncio
+async def test_add_series_does_not_duplicate_year(authenticated_client):
+    """Test that add_series doesn't duplicate year when name already contains it."""
+    response = await authenticated_client.post(
+        "/api/anime/add",
+        json={
+            "link": "https://aniworld.to/anime/stream/eighty-six",
+            "name": "86 Eighty Six (2021)"
+        }
+    )
+    
+    assert response.status_code == 202
+    data = response.json()
+    
+    # Folder should contain year only once
+    folder = data["folder"]
+    assert folder.count("(2021)") == 1
+
+
 @pytest.mark.asyncio
 async def test_add_series_returns_missing_episodes(authenticated_client):
     """Test that add_series returns loading progress info."""

tests/integration/test_series_parsing_edge_cases.py

@@ -495,6 +495,20 @@ class TestNameWithYearProperty:
         assert "(2013)" in sanitized
         assert "Attack on Titan" in sanitized
 
+    def test_name_with_year_does_not_duplicate(self):
+        """Test that name_with_year doesn't duplicate year."""
+        serie = Serie(
+            key="eighty-six",
+            name="86 Eighty Six (2021)",
+            site="aniworld.to",
+            folder="86 Eighty Six (2021)",
+            episodeDict={},
+            year=2021
+        )
+        
+        assert serie.name_with_year == "86 Eighty Six (2021)"
+        assert serie.name_with_year.count("(2021)") == 1
+
 
 class TestEnsureFolderWithYear:
     """Test Serie.ensure_folder_with_year method."""