AI/Infra: Add support for Leela Chess Zero (Lc0) backend analysis

[chinweobtagaz]

Description

While Stockfish is the strongest engine, Leela Chess Zero (Lc0) plays more 'human-like' positional chess, which many players prefer for training.

What Needs to be Done

• Provision GPU workers capable of running Lc0 backends.
• Wrap the Lc0 binary in the same orchestrator protocol as the existing Stockfish worker.
• Provide users a UI toggle to select their preferred AI opponent architecture.

Acceptance Criteria

• Lc0 can be selected as the backend engine for unrated bot matches.
• GPU orchestration successfully allocates Lc0 tasks without crashing.
• PGNs denote which engine was used in the metadata.