Run sync in a loop

@Withalion is already working on this.

Since Aug 28, 2026.

Following https://github.com/MerginMaps/product/issues/83, let's introduce the sync loop

```
local_changes = true

while (local changes):
pull_project()
push_state = push_project()

if push_state == success:
local_changes = get_remaining_changes()
clear retry counter
else if push_state is error, but can be retried:
sleep()
increment retry counter
else (push_state can not be retried || I have retried max times)
break
```

Acceptance criteria:
- On "Somebody else is syncing" error, the app retries to sync
- Sync works as before