Support default effort level in settings.json

Summary

Allow setting a default effort level (low, medium, high) in settings.json, so users don't have to manually run /model every session.

Current Behavior

• Default model can be configured in settings.json via "model" field
• Effort level can only be changed manually via /model command per session
• No way to persist effort preference across sessions

Proposed Behavior

Add "effort" field to settings.json (user-level and project-level):

{
  "model": "claude-opus-4-6",
  "effort": "low"
}

This would set the default effort when a session starts. Users can still override with /model during the session.

Scope: user settings (~/.claude/settings.json) and project settings (.claude/settings.json), with project taking precedence — same as model.

Why

Different workflows benefit from different effort levels. Power users who primarily do quick edits/questions want low by default. Users doing complex architecture work want high. Currently this requires manual action every session.

🤖 Generated with Claude Code