feat: render user content as markdown option (#16358)

feat: render user content as markdown option (#16358)

* feat: render user content as markdown option
- Add a persisted 'renderUserContentAsMarkdown' preference to the settings defaults and info metadata so the choice survives reloads like other options
- Surface the new 'Render user content as Markdown' checkbox in the General section of the chat settings dialog, beneath the PDF toggle
- Render user chat messages with 'MarkdownContent' when the new setting is enabled, matching assistant formatting while preserving the existing card styling otherwise
- chore: update webui build output

* chore: update webui build output