Fixes https://gitea.com/gitea/gitea-mcp/issues/187
The `due_on` argument was declared in the `milestone_write` schema but never read by `createMilestoneFn` or `editMilestoneFn`, so `opt.Deadline` was always nil and the field was silently dropped. This reuses the existing `params.GetOptionalTime` helper that already handles the analogous `deadline` field on issues and pull requests.
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This PR was written with the help of Claude Opus 4.7
Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/189
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>
silverwind