webui: minor settings reorganization and add disable autoscroll option

[ServeurpersoCom]

Summary

Adds a "Display" settings section grouping all visualization preferences, and introduces a disableAutoScroll option to address #17292.

Changes

• Created "Display" section consolidating 7 display-related settings
• Added disableAutoScroll toggle to prevent automatic scrolling during message streaming
• Maintains backward compatibility (auto-scroll enabled by default)

Motivation

While I couldn't reproduce the reported issue, this option is valuable for several use cases:

• Reading long responses without scroll interruption (issue Misc. bug: WebUI auto-scrolling disrupts reading #17292)
• Developer workflow: focusing on specific sections like thinking/reasoning output that aggregates during inference (relevant for MCP client in development)
• Manual viewport control during multi-turn conversations

This is a common UX pattern missing from most chat interfaces, giving users control while keeping the default behavior unchanged.

The new "Display" section also improves settings organization: the "General" section was overloaded, and we had a "Reasoning" section with only one display-related option. Grouping all visualization preferences together creates better balance and discoverability.

Closes #17292

[ServeurpersoCom]

Test :
https://github.com/user-attachments/assets/28f3a47d-3686-4b41-a0a2-eb0d4c7a6fdc