The Grist API requires all filter values to be arrays. This change adds
automatic normalization of filter values in get_records, wrapping single
values in lists before sending to the API.
This fixes 400 errors when filtering on Ref columns with single integer IDs.
Changes:
- Add filters.py module with normalize_filter function
- Update get_records to normalize filters before API call
- Add Orders table with Ref column to mock Grist server
- Add filter validation to mock server (rejects non-array values)
- Fix shell script shebangs for portability (#!/usr/bin/env bash)
