feat(console): add public Codex setup shell

[jmagar]

Summary

• add a public /setup page rendered with the real Gateway Console shell, AppHeader, and ConsoleHero
• make public setup mode avoid protected gateway-status polling while preserving normal authenticated shell behavior
• default the setup flow to Codex and support a same-origin /setup asset prefix for Worker-hosted deployment
• teach the bundle budget checker to normalize prefixed /_next/ asset paths

Verification

• targeted ESLint: clean
• console status tests: 5/5 passing, including a regression test proving public setup mode does not poll protected APIs
• full Next.js static export: 65 pages, including /setup
• TypeScript: clean
• bundle budgets: / 438.8 KiB, /gateway 372.9 KiB, /gateways 357.3 KiB compressed
• static build ID verified: df0026d
• live Worker deployment verified at https://labby.dinglebear.ai/setup/
• /setup, embedded guide, JSON, and /setup/_next assets return 200; root and OAuth routes remain owned by Labby

Deployment note

The current Cloudflare Worker serves only labby.dinglebear.ai/setup* and uses the exported real ConsoleShell page. The inner guide is same-origin at /setup/content?embed=1.