Support Sonnet, GPT-5.6 Luna, and GPT-5.6 Terra model families

[tlmader]

Problem

pstack accepts only Fable, Sol, Grok, and Opus in its model matrix.

Codex can run Luna and Terra. Claude can run Sonnet. setup-pstack rejects descriptors for these models.

Users cannot assign faster or lower-cost models to exploration and swarm roles through supported configuration.

Issue #33 tracks active-family selection. This change must not force every installation to probe all supported families.

Desired outcome

Support these provider-qualified model families in configuration, validation, dispatch, probes, and behavioral smoke tests:

• codex:gpt-5.6-luna@<effort>
• codex:gpt-5.6-terra@<effort>
• claude:sonnet@<effort>

Keep the parent-owned route. Codex models run natively on a Codex parent. Claude models run natively on a Claude Code parent.

Add the Claude-native Sonnet agent definitions that the route requires. Do not add a weaker-model fallback.

Acceptance criteria

• Given a sheet uses Luna, Terra, or Sonnet, when setup-pstack validates it, then the descriptor is valid for a supported effort.
• Given a new family is active, when setup-pstack probes it, then the requested model and effort run through the parent-owned route.
• Given a supported family is inactive, when setup runs, then setup does not require a probe for that family.
• Given setup writes an unchanged valid sheet, when setup runs again, then the sheet and parent integration remain byte-identical.
• Given an existing Fable, Sol, Grok, or Opus configuration, when setup runs, then its current routing behavior remains unchanged.
• Given a configured Luna, Terra, or Sonnet role, when a behavioral smoke runs, then its receipt or native transcript proves the selected route.