v0.2.0 — date-window filtering on list_entries

Add optional since_days, published_after, published_before params to list_entries_tool for date-windowed queries. Filters on datetime(COALESCE(published, created_at)) so null-published entries window by ingest time and mixed on-disk timestamp formats normalize correctly. Backward-compatible (MINOR). Spec: .specify/specs/001-entry-date-window/spec.md.