Allow Claude to change model/effort settings programmatically via tool or settings

Currently, the /model command is an interactive CLI-only command. There's no way for Claude itself to change the model or effort level mid-session, or to set effort level via settings.json.

Feature request:

1. Expose a way to set the effort level in settings.json (similar to how model can be set there)
2. Optionally, allow Claude to suggest or switch models/effort via a tool call, so it can adapt to task complexity without the user needing to intervene

Use case: Power users who want Claude to autonomously manage its own resource usage based on task complexity.