Add chat:cycleEffort action for single-key effort switching

Summary

Currently, switching reasoning effort requires opening the model picker (chat:modelPicker) and then using modelPicker:increaseEffort/modelPicker:decreaseEffort — a minimum of 3 keystrokes.

Request

Add a chat:cycleEffort action in the Chat context that cycles through effort levels (low → medium → high → max → low) with a single keystroke, similar to how chat:cycleMode cycles through input modes.

Use case

Power users frequently adjust effort mid-session. A single-key cycle (e.g. bound to tab) would make this as fast as shift+tab for mode switching. The current picker workflow is fine for model selection but overkill for just bumping effort up or down.