* Add pref and backend support for tab organization model key
Introduce kBraveAIChatTabOrganizationModelKey pref (default:
"chat-automatic") to allow users to choose which model is used
for tab organization. Update CreateTabOrganizationEngineIfNeeded
to read from this pref with fallback to "chat-automatic". Add
unit test for the invalid key fallback path.
* Add tab organization model selector in settings UI
Extract shared LeoModelSelector Lit component from personalization
page. Add tab organization model dropdown that appears when the tab
organization feature flag and pref are both enabled. Gate the tab
organization toggle behind the feature flag. Add localized string
for the model selector label.
* Improve tab focus prompts
When testing local model, found gemma tends to reply topics like
"['📰 News', '💻 Web Development', ... ]" which is failed to be parsed
because of the usage of single quotes on strings.
Improve tab focus prompts to mention valid JSON array and examples for
model to follow.
Jocelyn Liu
acf20dfedb