feat: Add API endpoint for managing categories

tests/api/test_categories_api.py

@@ -0,0 +1,32 @@
+import pytest
+from httpx import AsyncClient
+
+pytestmark = pytest.mark.asyncio
+
+
+async def test_get_categories_seeded_defaults(client: AsyncClient):
+    # Retrieve categories and verify the default list is present (since lifespan seeds them)
+    response = await client.get("/api/v1/categories")
+    assert response.status_code == 200
+    categories = response.json()
+    assert len(categories) >= 8
+
+    names = [c["name"] for c in categories]
+    assert "Food" in names
+    assert "Shopping" in names
+    assert "Travel" in names
+    assert "Other" in names
+
+
+async def test_create_and_duplicate_category(client: AsyncClient):
+    # 1. Create a new category
+    response = await client.post("/api/v1/categories", json={"name": "Medical"})
+    assert response.status_code == 201
+    data = response.json()
+    assert "id" in data
+    assert data["name"] == "Medical"
+
+    # 2. Try creating the same category (duplicate, case-insensitive check)
+    dup_response = await client.post("/api/v1/categories", json={"name": "medical"})
+    assert dup_response.status_code == 400
+    assert "already exists" in dup_response.json()["detail"]