fix(agent): clamp aux Ultra effort for Codex and xAI Responses

[BillyNour]

Summary

• Clamp Hermes Ultra (and sibling above-high labels) on the auxiliary Codex/Responses adapter so side-LLM calls match each backend's accepted effort ceiling.
• GPT-5.6 Codex path: ultra → max.
• xAI Responses path: ultra / xhigh / max → high.
• Stamp current_issuer_kind when building aux Responses input so foreign encrypted reasoning is dropped (same intent as main Codex transport).
• Tests cover GPT-5.6 ultra→max, xAI ultra/xhigh/max→high, and foreign encrypted-reasoning drop.

Why

Hermes product label Ultra is not a universal wire value. Aux calls that forwarded it raw could 400 or mis-route on Codex/xAI Responses. Main agent transport already clamps; aux did not fully match.

Test plan

• scripts/run_tests.sh tests/agent/test_auxiliary_client.py -q → 174 passed on exact head
• Independent leaf review on exact SHA (see PR comment / local evidence)

Scope

Only:

• agent/auxiliary_client.py
• tests/agent/test_auxiliary_client.py

No Honcho / installer changes.

[BillyNour]

Rebase onto current main

Pre: f43f9f89955a → New: 9d5a2fbbaecf
No review comments were open. Clean rebase only (2 files unchanged in scope).

@teknium1 still available for first review when convenient.

[teknium1]

Update on the effort-clamp half: the reasoning-effort translation was centralized on main (PR #90350 — canonical ladder + declared per-route vocabularies in agent/reasoning_effort.py, with per-model Codex vocabularies following in #90441), and the auxiliary client's Responses path now clamps through the shared policy including a per-model ceiling. That covers this PR's effort-clamp intent; the xAI ceiling for the aux path is a one-line vocabulary pick if the aux client ever targets xAI Responses directly.

The OTHER half of this PR — the issuer-kind stamps for replayed encrypted reasoning in _chat_messages_to_responses_input — is NOT covered by main and still looks valuable. Recommend rebasing this PR down to just that half so it can be reviewed on its own merits.