Adds a `set_fields` option to `extract.merge.gff_json` rules: forces existing Int fields to a fixed value on every extract, applied after preserve_fields/merge_lists so the forced value always wins. Fields absent from the document stay absent. Rule targets can now be globs (e.g. `areas/*.are.json`). Motivation: sow-module area weather chances must stay 0 (scripted regional weather owns weather); this makes the extract pipeline enforce it instead of a post-extract script. Covered by `TestExtractSetsConfiguredGFFJSONFields`; `make check` passes. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Reviewed-on: #40 Co-authored-by: vickydotbat <vickydotbat@tutamail.com> Co-committed-by: vickydotbat <vickydotbat@tutamail.com>