fix(desktop): respect validated server model recommendation

[neurogen-dev]

Problem

Windows Desktop setup preferred listed Sol even when the authenticated server catalog recommended another model. This prevented reliability recommendations from taking effect.

Change

Use the validated server default for Desktop setup. macOS already did this; preserve its behavior and add matching regression coverage. Keep user plugins/MCP/preferences and credential helpers intact.

Verification

• Windows actual selection/rendering regression: Sol listed first, default Luna -> Luna; regression fails on previous code.
• Sol-only, unavailable-Sol and invalid-default cases covered.
• Full macOS installer/catalog/rollback/concurrency smoke PASS.
• Windows Desktop/syntax/catalog/first-run mocks PASS, static/TOML/ShellCheck/diff checks PASS.
• Independent review CLEAR. Native Windows DPAPI/client gate runs in CI.
• Runtime catalog Luna default independently verified on Pilot/Optimal/Smart. Fresh genuine Codex 0.160 Luna HTML/shell task through NeuroAPI PASS9.2s without plugin ChatGPT requests.

No GUI runtime qualification is implied by configuration tests.