Apply Codex reasoning defaults in dashboard spawn flows

[khaliqgant]

Summary

• expose Codex reasoning metadata from /api/models and clamp stale saved defaults to supported models
• build Codex spawn commands with the correct default reasoning-effort override in the spawn modal
• preserve reasoningEffort when the dashboard uses the cloud workspace spawn path

Verification

• npm test -w @agent-relay/dashboard -- SpawnModal.test.tsx model-options.test.ts cloudFetchAdapter.test.ts
• npm test -w @agent-relay/dashboard-server -- proxy-server.test.ts
• npm run build -w @agent-relay/dashboard
• npm run build -w @agent-relay/dashboard-server

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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