🎨 Palette: Add aria-hidden to decorative FontAwesome icons

[ErisonBarros]

💡 What: Added aria-hidden="true" to embedded HTML tags containing GitBook textual icon fallbacks in aula-2.md.
🎯 Why: GitBook often embeds textual fallbacks inside tags (e.g. ✉️). Hiding them from screen readers prevents disruptive reading of raw fallback text for decorative elements.
📸 Before/After: Visual change is invisible.
♿ Accessibility: Improved screen reader navigation flow.

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PR created automatically by Jules for task 7858412975730758000 started by @ErisonBarros

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