Desktop app: add saved model/reasoning presets with assignable hotkeys

Summary

Please add first-class saved model configurations in the Codex desktop app, with optional keyboard shortcuts for switching between them.

Use case

I regularly switch between model/reasoning combinations such as:

• Luna Max — GPT-5.6 Luna with Max reasoning
• Terra High — GPT-5.6 Terra with High reasoning
• Sol Medium — GPT-5.6 Sol with Medium reasoning

Today, switching requires opening the model controls and changing the model and reasoning level manually. I would like to save these as named presets and bind each preset to a configurable hotkey.

Proposed behavior

• Add a Settings UI for creating, editing, deleting, and reordering named model presets.
• A preset should bundle at least the model and reasoning effort.
• Show saved presets alongside the raw model/reasoning options in the model picker.
• Allow each preset to have an optional keyboard shortcut.
• Applying a preset should update the active thread or next turn without discarding the current prompt or conversation context.
• Clearly show the active preset in the composer or status area.
• Respect account availability, workspace policy, and model rollout restrictions.

Why this would help

This would make it much faster to choose the right quality/latency tradeoff for a task while preserving preferred workflows. It would also avoid forcing users to configure model and reasoning settings separately.

Related requests:

• #9807 asks for a keyboard shortcut to switch models in the CLI/TUI.
• #14356 asks for dedicated reasoning-depth hotkeys.

This request is specifically about saved model+reasoning presets and native support in the Codex desktop app.