feat(settings): move session title config into Models settings

[bobleer]

Summary

• Move auto session title enablement and model selection from Session Personalization into the Models settings page.
• Extract a dedicated SessionTitleConfig component and update settings search/keywords plus en-US / zh-CN / zh-TW copy accordingly.
• Leave Session Personalization focused on Agent companion.

Test plan

• Open Settings → Models and confirm Auto Session Title appears with enable toggle and model selector.
• Toggle enable and change the title model; reload settings and verify persistence.
• Open Settings → Session Personalization and confirm session title UI is gone; Agent companion still works.
• Search settings for "session title" / "auto title" and land on Models.
• Switch locale among en-US / zh-CN / zh-TW and verify labels.