Add simple model configuration command and new model notifications

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

## Problem

When Anthropic releases a new model (e.g., Opus 4.6), there's no obvious way to:

1. Know the new model is available
2. Switch to it as the default

Currently users must:

• Discover releases independently
• Manually create %APPDATA%\Claude\settings.json (Windows) or ~/.claude/settings.json
• Know the undocumented "model": "opus" setting

## Suggested improvements

1. claude config command - e.g., claude config set model opus
2. New model notifications - "Opus 4.6 available. Run /model opus to try it"
3. Interactive setup - claude setup that asks for preferred model
4. Document user settings file - Currently not in --help or docs

## Context

Discovered after assuming my project settings.local.json would handle model preferences - it doesn't. Required assistance to find the correct location and format.

Proposed Solution

1. claude config command - Allow setting defaults via CLI, e.g.:

• claude config set model opus
• claude config list to see current settings

1. New model notifications - On startup, show something like:

"Opus 4.6 now available. Run /model opus to try it"

1. Interactive setup - Add claude setup that walks through preferences including default model

1. Document the user settings file - Add to --help output and docs:

• Windows: %APPDATA%\Claude\settings.json
• Mac/Linux: ~/.claude/settings.json
• Available settings: model, etc.

1. Auto-upgrade option - Setting like "model": "latest-opus" that always uses the newest Opus release

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

Anthropic released Opus 4.6 on Feb 5, 2026. As a paying Claude Code max user, I wanted to upgrade immediately but:

1. Discovered settings.local.json model preferences don't work
2. Spent 20+ minutes finding the actual user settings location
3. Had to manually create %APPDATA%\Claude\settings.json
4. Wrote {"model": "opus"} based on trial and error

Expected: claude config set model opus or a prompt on startup saying "New model available"

Additional Context

_No response_