feat: strengthen backup and mobile workflows

tests/test_after_completion_recurrence.py

@@ -242,7 +242,7 @@ def test_after_completion_recurrence_survives_json_and_csv_round_trips(client):
     assert recurrence["after_completion_days"] == 2
     assert recurrence["last_completed_at"] is None
 
-    restored = client.post("/api/v1/restore?mode=replace", json=exported)
+    restored = client.post("/api/v1/restore?mode=merge", json=exported)
     assert restored.status_code == 200
     restored_task = client.get("/api/v1/tasks", params={"q": task["title"]}).json()["items"][0]
     restored_recurrence = client.get(f"/api/v1/tasks/{restored_task['id']}/recurrence").json()
@@ -252,7 +252,7 @@ def test_after_completion_recurrence_survives_json_and_csv_round_trips(client):
     csv_export = client.get("/api/v1/export.csv")
     assert csv_export.status_code == 200
     csv_restore = client.post(
-        "/api/v1/restore.csv?mode=replace",
+        "/api/v1/restore.csv?mode=merge",
         files={"file": ("dodo-export.csv", csv_export.content, "text/csv")},
     )
     assert csv_restore.status_code == 200