fix: toolbar demo toggle buttons not toggling off

[AnttiJalomaki]

Summary

• Fix toolbar demo where bold/italic/underline buttons only toggled ON but never OFF
• Add visual pressed state indication to toolbar buttons

Root Cause

The original demo had two issues:

1. Broken toggle logic: The toggle_style function called retain() to remove the style, then unconditionally push() to re-add it - making toggle OFF impossible
2. Reactive subscription issue: Passing a use_memo value directly to the style attribute didn't properly subscribe in the reactive context, so style changes weren't reflected in the DOM

Solution

• Replaced Vec-based state with individual Signal<bool> for each style, using .toggle()
• Used Dioxus's native CSS-in-RSX individual properties (font_weight, font_style, text_decoration, text_align) instead of a computed style string
• Reading signals directly in RSX conditionals ensures proper reactive subscriptions
• Added data-state attribute and CSS for visual button pressed state

Test plan

• Same for Italic and Underline
• Click Bold again → text returns to normal, button shows unpressed state
• Multiple styles can be combined and individually toggled
• Click Bold → text becomes bold, button shows pressed state
• Alignment buttons work and show active state

[github-actions]

Preview available at https://dioxuslabs.github.io/components/pr-preview/pr-192/