sync: reconcile rustnzb monorepo drift

[thedancingdeveloper]

Summary

• reconcile the standalone crate with rustnzb/crates/nzb-core through monorepo release/v1.3.9 (60c5bb4)
• carry newer configuration, database/history/statistics, NZB parsing, group database, and SABnzbd import behavior into the independent crate
• require the released nzb-nntp 0.2.23 API and bump this crate to 0.2.17

Validation

• formatting, all-feature locked check, strict all-target Clippy
• full test suite: 116 passed
• cargo package --allow-dirty verified

Migration / dependency automation

• canonical native-transfer target verified under TheDancingDeveloper-org
• weekly Cargo and GitHub Actions Dependabot configuration present
• vulnerability alerts and automated security fixes enabled