REF-028: Audit current MbedTLS 4.1 integration

[itlezy]

Imported backlog item REF-028.

• Lane: Security and Operations
• Type: Refactor
• Priority: Minor
• Release: unscheduled
• Local spec: https://github.com/emulebb/emulebb-tooling/blob/main/docs/active/items/REF-028.md

This issue is the authoritative workflow record. The linked local document is retained as an engineering spec/evidence record.

Before implementation, revalidate this slice against current main, current dependency pins, and WORKSPACE-POLICY.md.

[itlezy]

Closing as not planned for eMuleBB MFC.

The MFC client is frozen at the 0.7.3 / 0.7.x line with only very narrow critical maintenance and non-behavior-expanding support diagnostics/instrumentation accepted. The 0.7.3 MFC + aMuTorrent release is the frozen release line; future product work is no longer tracked against the MFC app.

If a concrete critical 0.7.x crash, data-loss, security, or release-support issue appears later, open a new narrowly scoped maintenance issue with current reproduction/evidence.