- `null` means "Any weight"
- `-1` means "No weight"
- 0 now means "0 weight"
- Update frontend weight dropdown
- Update backend weight filters
- Add failing tests for weight values
- Fix weight selection for no / any / 0 weight
- Fix issue filtering by weight
- Modify IssuesFinder for no-weight filtering
- Update tests for 'any' filter to include all issues regardless
of weight (even no weight)