[FEATURE] Per-query effort level with auto-revert

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

Summary

Add the ability to set effort level for a single query, automatically reverting to the previous level afterward.

Use case

When working in interactive mode at medium effort, occasionally a complex question needs high or max effort. Currently you must manually /effort high, ask the question, then
/effort medium — easy to forget the revert.

Proposed Solution

A syntax like:

• /effort high --once — apply to next query only
• claude --effort-once high — in -p mode
• Or a keyboard shortcut that temporarily boosts effort for one turn

Alternative Solutions

• Skills can't modify session settings
• Hooks can't change effort programmatically
• Manual toggle works but is error-prone

Priority

High - Significant impact on productivity

Feature Category

Interactive mode (TUI)

Use Case Example

1. I have a question which requires high effort
2. Then I move to lots of simple questions.
3. I will waste a lot of time and tokens because I would have forgetten to switch back to low effort.

Additional Context

_No response_