Add GPT-5.6 Sol, Terra, and Luna model support

[byapparov]

Context

OpenAI and models.dev now list GPT-5.6 Sol, Terra, and Luna, but the CLI's Codex OAuth allow-list and OpenAI reasoning variants do not expose their complete model-specific effort levels.

Goal

Make all three models available through OpenAI API-key and Codex OAuth authentication with correct effort and context metadata.

User story

As an aictrl CLI user, I want to select GPT-5.6 Sol, Terra, or Luna with the efforts supported by my authentication path.

Proposed approach

Update the model fixture, OpenAI variant generation, and Codex OAuth filtering while keeping live models.dev data authoritative.

Acceptance criteria

• API-key models expose none, low, medium, high, xhigh, and max.
• Codex OAuth exposes Sol/Terra through ultra and Luna through max; ultra sends max on the wire.
• OAuth models use the supported 272k input and 128k output limits with subscription costs zeroed.
• Focused tests, package tests, typecheck, formatting, and build pass.

Out of scope

• Adding new proactive multi-agent orchestration semantics for ultra.
• Advertising the models through gateways that do not publish them.

Risks and dependencies

• Availability depends on OpenAI and models.dev continuing to publish these model IDs.

Open questions

• None.