Add "ultra" reasoning level for Codex GPT-5.6 Sol and Terra, and expose
Max for Luna (Luna falls back Ultra to Max since it is not supported
upstream). Scoped to cx/ routes only; Kiro and generic OpenAI routing
unchanged.
- map service_tier=fast to upstream priority; drop unsupported tiers
- normalize reasoning effort max to xhigh (codex-only)
- convert 200-SSE model-capacity errors into 503 so account fallback rotates
- keep normal SSE output intact after peeking
Co-authored-by: Cursor <cursoragent@cursor.com>