refactor(tests): use client fixture for test isolation

Replace all AsyncClient instantiations in test_sources.py and test_jobs.py
with the shared  fixture from conftest.py. This ensures proper test
database isolation via dependency overrides.

- Remove imports of httpx AsyncClient, ASGITransport, and app
- Add client fixture parameter to all test functions
- Remove async with blocks around HTTP requests
- test_engine.py already uses db fixture correctly, no changes needed

backend/tests/test_sources.py

@@ -1,15 +1,12 @@
 import pytest
-from httpx import AsyncClient, ASGITransport
-from app.main import app
 
 @pytest.mark.asyncio
-async def test_create_source():
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        response = await ac.post("/api/sources/", json={
-            "name": "Test Source",
-            "type": "local",
-            "config": {"path": "/tmp/test"}
-        })
+async def test_create_source(client):
+    response = await client.post("/api/sources/", json={
+        "name": "Test Source",
+        "type": "local",
+        "config": {"path": "/tmp/test"}
+    })
     assert response.status_code == 200
     data = response.json()
     assert data["name"] == "Test Source"
@@ -17,83 +14,75 @@ async def test_create_source():
     assert "id" in data
 
 @pytest.mark.asyncio
-async def test_list_sources():
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        # Create source first
-        await ac.post("/api/sources/", json={
-            "name": "Test Source",
-            "type": "local",
-            "config": {"path": "/tmp/test"}
-        })
-        
-        response = await ac.get("/api/sources/")
+async def test_list_sources(client):
+    # Create source first
+    await client.post("/api/sources/", json={
+        "name": "Test Source",
+        "type": "local",
+        "config": {"path": "/tmp/test"}
+    })
+    
+    response = await client.get("/api/sources/")
     assert response.status_code == 200
     data = response.json()
     assert len(data) >= 1
 
 @pytest.mark.asyncio
-async def test_get_source():
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        create_resp = await ac.post("/api/sources/", json={
-            "name": "Test Source",
-            "type": "local",
-            "config": {"path": "/tmp/test"}
-        })
-        source_id = create_resp.json()["id"]
-        
-        response = await ac.get(f"/api/sources/{source_id}")
+async def test_get_source(client):
+    create_resp = await client.post("/api/sources/", json={
+        "name": "Test Source",
+        "type": "local",
+        "config": {"path": "/tmp/test"}
+    })
+    source_id = create_resp.json()["id"]
+    
+    response = await client.get(f"/api/sources/{source_id}")
     assert response.status_code == 200
     assert response.json()["id"] == source_id
 
 @pytest.mark.asyncio
-async def test_delete_source():
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        create_resp = await ac.post("/api/sources/", json={
-            "name": "Delete Me",
-            "type": "local",
-            "config": {"path": "/tmp/test"}
-        })
-        source_id = create_resp.json()["id"]
-        
-        response = await ac.delete(f"/api/sources/{source_id}")
+async def test_delete_source(client):
+    create_resp = await client.post("/api/sources/", json={
+        "name": "Delete Me",
+        "type": "local",
+        "config": {"path": "/tmp/test"}
+    })
+    source_id = create_resp.json()["id"]
+    
+    response = await client.delete(f"/api/sources/{source_id}")
     assert response.status_code == 200
     
     # Verify deletion
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        get_resp = await ac.get(f"/api/sources/{source_id}")
+    get_resp = await client.get(f"/api/sources/{source_id}")
     assert get_resp.status_code == 404
 
 @pytest.mark.asyncio
-async def test_update_source():
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        create_resp = await ac.post("/api/sources/", json={
-            "name": "Original Name",
-            "type": "local",
-            "config": {"path": "/tmp/test"}
-        })
-        source_id = create_resp.json()["id"]
-        
-        response = await ac.put(f"/api/sources/{source_id}", json={
-            "name": "Updated Name"
-        })
+async def test_update_source(client):
+    create_resp = await client.post("/api/sources/", json={
+        "name": "Original Name",
+        "type": "local",
+        "config": {"path": "/tmp/test"}
+    })
+    source_id = create_resp.json()["id"]
+    
+    response = await client.put(f"/api/sources/{source_id}", json={
+        "name": "Updated Name"
+    })
     assert response.status_code == 200
     assert response.json()["name"] == "Updated Name"
     assert response.json()["type"] == "local"  # Unchanged
 
 @pytest.mark.asyncio
-async def test_get_source_not_found():
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        response = await ac.get("/api/sources/99999")
+async def test_get_source_not_found(client):
+    response = await client.get("/api/sources/99999")
     assert response.status_code == 404
 
 @pytest.mark.asyncio
-async def test_update_source_not_found():
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        response = await ac.put("/api/sources/99999", json={"name": "Test"})
+async def test_update_source_not_found(client):
+    response = await client.put("/api/sources/99999", json={"name": "Test"})
     assert response.status_code == 404
 
 @pytest.mark.asyncio
-async def test_delete_source_not_found():
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        response = await ac.delete("/api/sources/99999")
+async def test_delete_source_not_found(client):
+    response = await client.delete("/api/sources/99999")
     assert response.status_code == 404