Closes #54313

**Before:**
- Favoriting a model only stored `provider`, `model`, and hardcoded
`enable_thinking` to `false`.
- Selecting a favorited model would not restore your preferred
`enable_thinking`, `effort`, or `speed` settings.

This means that if you'd like to use, say, GPT 5.4 your favorite model
on `xhigh` effort every single time, switching to it would set effort to
`medium` (the default for the model) instead.

**After:**
- Favoriting a model captures your current `enable_thinking`, `effort`,
and `speed` when it matches the currently-selected model. Otherwise, it
falls back to the model's own defaults, i.e. thinking-capable models are
no longer favorited with `enable_thinking` forced to `false`.
- Selecting a favorited model applies its stored thinking / effort /
speed.
- Toggling thinking, changing effort, or toggling fast mode on a
favorited model updates the favorite entry in settings (along with the
existing `default_model` setting), so the preference doesn't drift.

Release Notes:

- Agent favorite models now remember and restore per-model thinking,
effort level, and fast mode preferences.