Preserve .max(1) guard in WireframeServer::new to ensure at least one worker

[coderabbitai]

Summary

WireframeServer::new used to apply .max(1) to the default returned by num_cpus::get(), guaranteeing at least one worker task. The recent refactor removed this guard.

Context

• Requested by @leynos during review of PR Fix compile errors and clippy #11
• Earlier discussion: Ensure WireframeServer::new enforces minimum worker count of at least 1 #12 (similar topic)

Acceptance Criteria

• Constructor again guarantees a minimum of 1 worker (or equivalent logic).
• Unit test (or doc-test) covers the zero-CPU edge case, if feasible.