Keybindings: actions to directly set model, effort level, and ultracode

Feature request

~/.claude/keybindings.json currently offers only chat:modelPicker for model selection. I'd like single-keystroke bindings for:

• Setting a specific model, e.g. app:setModel:fable / opus / sonnet / haiku (so I can bind alt+f, alt+o, alt+s, alt+h)
• Setting a specific effort level, e.g. app:setEffort:low|medium|high|xhigh|max (bindable to alt+1–alt+5)
• Toggling ultracode, e.g. app:toggleUltracode

A generic "bind a key to a slash command" mechanism (e.g. "alt+h": "/model haiku") would cover all of these and more.

Use case: switching between Fable for hard work and Haiku for cheap loops many times a day; the picker flow (meta+p + navigation) is several keystrokes each time.